Install all *.lua files instead of only init.lua
Return a lua table instead of just ffi userdata

cephes is now a proper lua table, with a single field
`cephes.ffi` which is the `userdata` ffi namespace.
All indexing is passed to this namespace if it does not exist
in the lua table. This allows for safety wrappers.
Ignore build directory
Add light Lua wrappers to show the functions

The user will thus be able to see which functions exist by simply
examining the cephes table. FFI objects do not offer this possibility.
Merge branch 'errControl' into ffiParsing