The curl library should be build in release mode for release versions

[isaacvr]

Describe the bug
The build type is hard coded.

Environment information:

• Any

Steps to Reproduce
Just look at the code https://github.com/simelo/libskycoin/blob/3cb637dbd49eb3073d18b25205cc58e2519a28c7/lib/curl/CMakeLists.txt#L9

Actual behavior
The curl library is build in debug as unique option.

Expected behavior
Be able to set a predefined value via command line.

Additional context
It's very important to move on this if you regenerate the CMakeLists.txt file.