OpenResty OPM Compatibility and Upload

[billythedummy]

Changes:

• Created dist.ini to support building lib as an OpenResty OPM package

• Moved source files into lib folder because OPM package builder adds all subdirectories; specifying lib_dir as top level directory in dist.ini causes the test folder to be included as well.
  I have not used luarocks before so I did not touch the .rockspec file. Might need to change some stuff there.

• As a result, changed package.path of test/test.lua from ../?.lua; to ../lib/?.lua;

• Edited .gitignore to ignore files created by opm build

I hope I got the credentials right in dist.ini. In the meantime, I hope you don't mind the fact that I've uploaded a copy of the package onto OPM under my github handle: billythedummy/SLAXML. Please let me know when you've merged the changes and pushed your build onto OPM, and I'll take it down. I do not wish to contribute to OPM bloat lol