Add a keyword feature similar to common lisp or racket

[Collin McKinley]

This is something that has been possible in crow for a while, just without its own special syntax. Create a way to define variables within a function call like (function "argument" :value 123). For this i think the Common Lisp style syntax would be best, since the square brackets [] are probably going to be used for the object oriented function call portion of Crow.

In the example given above, the variable value would be created and given 123 as its value. To check if this actually happened, one could run (if (defined (current-scope value)))