Implement miscellaneous standard lua functions

[bananu7]

The list is here. A few of those are already done:

• assert
• collectgarbage - Add GC #57
• dofile, loadfile - this requires filesystem access, so probably will have to wait for Introduce filesystem capabilities #24
• error
• getfenv
• _G - _G evaluates to Nil #29
• getmetatable, setmetatable
• ipairs, pairs - covered by Implement __pairs and __ipairs #37 ?
• load - but see Add missing parameters to load (source, env) #85
• loadstring
• next
• pcall
• print - needs Introduce stdio capabilities #23
• rawequal - rawlen/rawget etc. #72
• rawget - rawlen/rawget etc. #72
• rawlen - rawlen/rawget etc. #72
• rawset
• select - Select function & call spill added #67
• tonumber - Added tonumber #65
• tostring - Implement tostring and the metafunction #39
• type
• unpack
• _VERSION - rawlen/rawget etc. #72 as a bonus
• xpcall

[bananu7]

I wonder if e.g. assert could be implemented in pure Lua. This would require linking a Lua preamble to all VMs? Would that reside somewhere as a file to be pulled in to the build, or just a module with a big string inside?