Lexer: Greatly simplify scan_string.
Lexer: Greatly simplify scan_string.

The original idea was good: Use strcpy to copy over a string that's simple
instead of a byte-by-byte copy. However, doing so resulted in a complicated
maze of reallocs and copy downs.

In the end, it's simpler to just copy byte by byte all the time (roughly 1/3
the size it used to be). Part of that reduction is from some tricks I've
learned since I first put in the function too.

crasm/lily,boardwalk/lily,boardwalk/lily,crasm/lily,crasm/lily