update unit tests
update documentation
add => operator to lexer
add => to parser and refactor fn grammar
implement => and refactored fn grammar
Update documentation
allow _ in identifiers
add .gitignore
add support for hex literals
add concatenation (++) operator
improve some error messages
modify delbrot build order

Originally the Makefile was building the lexer (lex.yy.c) before the
parser (y.tab.c). This can cause problems if a new symbol is added to
the grammar, because flex gets its symbols from y.tab.h. Now, y,tab.h
is built first, so flex will not throw an unknown symbol error.
fix return macros
add lexing/parsing rules for plugins
add struct for handling libraries
add function for looking up library functions
add code to handle import statements
add generated files
add plugin directory and -ldl flag
add tools for creating plugins