added Lua 5.5 support + tests on CI

[luau-project]

Description

@moteus

• fixes Lua 5.5 support #17 mostly following Add. Support Lua 5.4 #15;
• Also added GitHub CI to run tests + code coverage (including cov upload) on latest Ubuntu, macOS and Windows.

Note

I didn't edit Travis CI and AppVeyor files, because the added GitHub CI includes everything. Perhaps, you may want to drop Travis CI and AppVeyor.

Changes

• Added Lua 5.5 support on development rockspec (lua-path-scm-0.rockspec);
• Added lua-path-0.3.1-3.rockspec supporting Lua 5.5;
• Fixed tests for Lua 5.5 preventing changes in the control variable. On Lua 5.5, the control variable (first variable of the for loop) became read-only (see https://www.lua.org/manual/5.5/manual.html#3.3.5);
• Added GitHub CI to run tests + code coverage (including cov upload) on latest Ubuntu, macOS and Windows;
• Added a build badge for GitHub CI on README.md.

PS

If you find these changes appropriate, please, upload lua-path-0.3.1-3.rockspec to LuaRocks website.