Rename folder chapter9-10 to main
Remove opsymbol, opword
Change symbol to regexp matching all printable chars
Add typedef for unction pointer lbuiltin
Additions to support function pointers
	lval_fun
	lval_copy
Add lenv type to support environment
	struct lenv
	lenv helper functions
Add builtin function support
Update builtin function signatures to support environment
Add def function to support variable definition
Add additional error reporting functionality to lval_err
	Format string for error arguments
Improve error handling for LASSERT_xxx macros
Add LASSERT_TYPE macro