New features:

• Allow pattern matching on multiple values.
• Add io.setformat, which allows us to set a default format for all echo statements.
• Add str->partition.
• Add format option for echo.
• Allow = syntax in tables.
• Add 'b' option to bool->tostr.
• Add bool->tobyte.
• Add table->setdefault.

C API:

• Add function to allow us to disable echo from the C API.
• Add YASL_getvargsstart to get us the starting index of the variadic arguments.
• Add YASL_floattostr to convert floats to string in the same way as float->tostr.