Make replayer code portable

[PoroCYon]

• Exported symbols are now the same (as seen from C) across all (supported) platforms (No leading underscore bullshit)
• section syntax differs a bit for NASM ELF output, now fixed.
• More stuff of that ilk

Basically the same procedure as in gopher-atz/4klang#2 , except I was able to test the exporter now as well.

[askeksa]

Thank you for figuring out all the various changes necessary to make the converter and player Linux compatible!

I might want to make some of the changes in a slightly different way, but I will go through them to figure out how they best fit in. I'll probably have some questions along the way...

[askeksa]

OK, I finally got around to looking through this PR and trying out the changes, both on Linux (Ubuntu 16.04) and Windows.

I have made several changes from your original proposal, which I will describe in the following. To begin with, I have added the commits (which are still attributed to you) on a branch, so you have a chance to look through them before I merge them to master: https://github.com/askeksa/Oidos/tree/portable_player

So here are the things I changed:

• Various minor changes to macro names and comments.
• Renamed play.c to dump_wav.c to match the produced executable.
• Section names on Windows are limited to 8 characters, so I changed some of them back and also changed the Windows macros to not add a prefix.
• nasm doesn't seem to pre-define symbols identifying the platform, so I changed the platform switch in platform.inc to %ifidn __OUTPUT_FORMAT__, win32 as suggested by the nasm manual.
• Defining ID3D11Texture2D_ID as a uint32_t array does not work with D3D11 code, which must have it as GUID, so I changed that back. Since it is guarded by #ifdef GUID_DEFINED, it should not disturb other platforms.
• In random.asm, I simply define and export both the undecorated and decorated versions of ID3D11Texture2D_ID instead of having it depend on the platform.
• I left out the renames of the conversion scripts. While I do realize that Linux conventionally uses all lowercase for files like this, it is not something that blocks them from being used, so for a cross-platform distribution, I prefer to leave them as they are. This also avoids breaking existing scripts.
• OidosUpgrade.py is just an internal script for converting pre-2.0 Oidos songs (of which there exist none which haven't already been converted), so there is not much point in maintaining it. Therefore, I left out that change.
• For the easy_elf feature, I merged it into easy_exe, so there's just one directory, now with an extra script in it. I also rewrote the script to work similarly to the Windows script (i.e. use a temp dir, delete temp files before rather than after).
• The last commit was merged into the first one, so we just use _WIN32 right away.

Do these changes seem reasonable to you?

[PoroCYon]

Yup, that all looks fine, no objections from me.

[askeksa]

Great. Thanks again for your contribution.