Macros (doesn't work yet)
Add some debugging code.
Add test.l and eval.log to .gitignore
Add debugging code to follow evaluation
Finish macro implementation

Macros are implemented as a special type of function that converts all
arguments into Q-expressions before evaluation proceeds.

Of the internal functions, only 'if', 'and', and 'or' are implemented as
macros. 'def', '\' and '^' are not.
Merge branch 'macros'