b2: document example + point to temporary fork

- Add documentation in storage-examples for using Perkeep with b2 as a
  storage backend. The documentation uses the new API terminology:
  AccountID is no longer a thing in the Backblaze web console.

- Temporarily replace FiloSottile/b2 by aviau/b2 where I host a copy of
  clgillis's Pull Request[1]. We can point to the original project
  again as soon as it is merged.

  Note that I haven't updated the vendor directory and it seems that
 `go mod vendor` updates way more things that are also outdated in the
  master branch, so I will leave that as an exercise to whoever has
  commit access :).

Before this Pull Request, launching the b2 storage would error with the
following error message:
```
Error parsing config: Caught panic: error instantiating storage for prefix "/sto-b2/", type "b2": Post "https://api000.backblazeb2.com/b2api/v1/b2_list_buckets": b2 remote error [bad_request]: accountId invalid
```

Now, it seems to work as expected!

1. FiloSottile/b2#8

Author: aviau

doc/storage-examples.md

@@ -6,17 +6,17 @@
 
 To use S3 with Perkeep, you need to:
 
-* Sign up for an Amazon Web Services account
-* Sign into the AWS console, navigate to 'S3'
-* Create an S3 bucket for your Perkeep backups (Perkeep will not work if you put other files in this bucket)
-* Configure your Perkeep server to sync blobs to the S3 bucket
+* Sign up for an Amazon Web Services account.
+* Sign into the AWS console, navigate to 'S3'.
+* Create an S3 bucket for your Perkeep backups (Perkeep will not work if you put other files in this bucket).
+* Configure your Perkeep server to sync blobs to the S3 bucket.
 
 It is advisable to use a dedicated key/secret for Perkeep:
 
-* Sign into the AWS console, navigate to 'Identity & Access Management' and click 'Users'
-* Click 'Create new users' and create a user for Perkeep (keep 'Generate an access key' checked)
+* Sign into the AWS console, navigate to 'Identity & Access Management' and click 'Users'.
+* Click 'Create new users' and create a user for Perkeep (keep 'Generate an access key' checked).
 * Click 'Show User Security Credentials' to get the users Access key and Secret key - these will be required to configure Perkeep and can't be obtained after you leave this screen.
-* Go back to the user list and select the new user, and on the 'permissions' tab add the following 'inline policy' (replacing YOUR_BUCKET_NAME with the name of the bucket you created)
+* Go back to the user list and select the new user, and on the 'permissions' tab add the following 'inline policy' (replacing YOUR_BUCKET_NAME with the name of the bucket you created):
 
 ```
 {
@@ -42,5 +42,29 @@ It is advisable to use a dedicated key/secret for Perkeep:
 
 Finally, add the s3 config line to your Perkeep `server-config.json`:
 ```
-s3: "ACCESS_KEY:SECRET_KEY:YOUR_BUCKET_NAME"
+"s3": "ACCESS_KEY:SECRET_KEY:YOUR_BUCKET_NAME"
+```
+
+## B2
+
+[Backblaze B2](https://www.backblaze.com/b2/cloud-storage.html) is simple, reliable, affordable object storage.
+
+To use b2 with Perkep, you need to:
+* Sign up for a Backblaze account.
+* Sign in to the Backblaze console, navigate to 'Buckets'.
+* Create a bucket for your Perkeep backups (Perkeep will not work if you put other files on this bucket).
+* Configure your perkeep server to sync blobs to the Backblaze bucket.
+
+It is advisable to create a dedicated Application Key for Perkeep:
+
+* Sign in to the Backblaze console, navigate to 'App Keys'.
+* Click 'Add a New Application Key'.
+* Give it a name, for example 'perkeep'.
+* Allow access to the bucket that you just created.
+* Choose 'Read and Write'.
+* Click 'Create New Key'.
+
+Finally, add the b2 config line to your perkeep `server-config.json`:
+```
+"b2": "keyID:applicationKey:bucket"
 ```

go.mod

@@ -71,3 +71,5 @@ require (
 )
 
 replace google.golang.org/grpc v1.14.0 => github.com/bradfitz/grpc-go v0.0.0-20170203184515-188a132adcfba339f1f2d5da52498451341f9ee8
+
+replace github.com/FiloSottile/b2 => github.com/aviau/b2 v0.0.0-20180913003434-1ae8d9b78db9

go.sum

@@ -9,6 +9,8 @@ github.com/FiloSottile/b2 v0.0.0-20170207175032-b197f7a2c317 h1:1GuMjC4tjfwnWBdo
 github.com/FiloSottile/b2 v0.0.0-20170207175032-b197f7a2c317/go.mod h1:3DBotXAz3n/g1px/orhrK7xBJLjfaJRRrsEAJiUYEtY=
 github.com/PuerkitoBio/goquery v1.5.0/go.mod h1:qD2PgZ9lccMbQlc7eEOjaeRlFQON7xY8kdmcsrnKqMg=
 github.com/andybalholm/cascadia v1.0.0/go.mod h1:GsXiBklL0woXo1j/WYWtSYYC4ouU9PqHO0sqidkEA4Y=
+github.com/aviau/b2 v0.0.0-20180913003434-1ae8d9b78db9 h1:qPlc4QTdYURXX4FHRpfJvbTvak1JzstfgJXdcB1nkCk=
+github.com/aviau/b2 v0.0.0-20180913003434-1ae8d9b78db9/go.mod h1:8dNRU5RV/wbLtEayj1Ayzi0zd2oxXlaneOBTD9rWYkw=
 github.com/aws/aws-sdk-go v1.14.31 h1:amhorvKh1zNxo9YCntvA5uDmgw+pCYXOp4xO8WS1oDg=
 github.com/aws/aws-sdk-go v1.14.31/go.mod h1:mFuSZ37Z9YOHbQEwBWztmVzqXrEkub65tZoCYDt7FT0=
 github.com/bradfitz/latlong v0.0.0-20140711231157-b74550508561 h1:mz4equOOUOnI4q5E7dyHlRx1x63YEaYwhlVluCDila4=