Version 2.2.1 - Forge addon and various fixes

Changes:

• New forge addon to install and run forge directly via the command line (#29).
• Extract HTTP part from json_request method to a common http_request function and added it to __all__.
• Added new replacement variables that seems supported by official launcher and used by forge installed metadata.
• When preparing version libraries, libraries with no URL are now defaulting to libraries.minecraft.net maven server.

Fixes:

• Fixed pretty logging file not being created if original one is not downloaded. The only issue is that no login configuration was loaded.
• Fixed a critical error in DownloadList.download_files() when non-OK HTTP status code was returned.

Download and install:

To install PortableMC, please read this repository README, the single-file script is available below in the portablemc-single archive.