v0.9b

Long time no see, eh? This is the ultimate expr overhaul, behold:

• Complete expr reimplementation from scratch using Flex/Bison instead of S.Y. algorithm
• Slight performance increase
• Add trunc
• Add sec, csc, arcsin, arccos, arcsec, arccsc and various different aliases for each.
• Removed -r option from the command (will probably return in the future. Just use include mathop in the meantime)
• IMPLICIT EXPR CALLING for all built-in functions
• IMPLICIT 0 RETURN for empty expressions
• General, non-expr related QoL improvements
• Updated docs