Fixes(/tests) from my fork

[thisismypassport]

Hi,

I've created a fork of z8lua (specifically, the pico8 branch) containing:

• Some tests for pico8 apis & syntax (not exhaustive)
• Some fixes to pico8 api issues
• Some missing syntax & missing apis (some of which you have explicitly decided not to include in your repo, so I don't expect you'll want to take everything)

You (and anyone else who wants it) can find the fork here:
https://github.com/thisismypassport/z8lua
(The goal of the fork is to be able to run pico8 "script" carts [like parens8] in shrinko8)
[note - I used to have something else in this fork, but I moved that to the zepto8 branch, which does NOT contain these fixes]

A detailed list of the fixes/additions, ordered roughly from most to least likely wanted by you:

• syntax - support nested shorthands
• syntax - support missing '?' expression (not just statement)
• syntax - support missing '~' as alias for '^^'
• syntax - support missing 'if .. do' (as alias for 'if .. then') syntax
• meta - fixed __rotr metamethod (thanks to siapran's issue for catching this)
• tonum - fix incorrect flag 0x2 implementation
• tonum - fix buffer overflow with flag 0x1
• tonum - support flag 0x4
• chr - support arbitrary number of parameters
• ord - do not fail for non-tables
• ord - [otherwise] always return the number of results requested
• split - fix for numeric strings to split by (should be treated as a string, not a number)
• sub - implemented (largely reusing lua's implementation)
• inext - exposed and changed its implementation to not fail for non-tables (applies also to the result of ipairs)
• pack/unpack - exposed (reusing lua's implementation)
• table apis - implemented add/del/deli/count/all/foreach
• memory - support 64k memory (instead of the old 32k)
• memory - implement the rest of the apis (not just the peek operators) - peek*/poke*/memcpy/memset.
• memory - allow use of peek/poke/etc out-of-the-box, without having to call special apis
• misc apis - exposed coroutine apis with pico8 names (largely untested, but should be roughly compatible)
• tests that cover a lot of the above (see 'test' subdirectory)
• [from this point on, things are no longer about pico8 compatibility, and so are even less likely to be wanted by you, including for completion's sake]
• lua apis - fix in io module (io & os module are untested but much should be working)
• tostr - support printing userdata
• c api - fixed compilation of certain expressions (e.g. lua_Number lua_Integer ; lua_Number double) under various windows environments by adding generic operators. [needed for certain usages of the C api - not for z8lua itself]
• c api - some changes and hacks to allow c<->lua code that uses luaL_ref/unref and lua_rawgeti/rawseti - to work with integers larger than 15K.

I'm happy to open a pull request if you let me know which changes you want me to include in it.