Add :compare-forms debug option

When specified on command line, e.g.:

    lein eastwood '{:debug #{:compare-forms}}'

Eastwood will write two files forms-read.txt and forms-emitted.txt,
each containing forms of the code being analyzed, pretty-printed, with
metadata shown.

form-read.txt contains the forms after they have been read, top-level
do forms are recognized and each subform analyzed separately, and
after calling macroexpand-1 on them, at the top level only.

forms-emitted.txt contains the forms after all of the above steps,
plus being analyzed with tools.analyzer(.jvm) to produce an AST, and
then emit-form called on the AST to produce a form.

The intent is to make it straightforward to compare these two files,
and look for issues.  There are still many differences between these
forms that are likely normal and acceptable, so it is recommended to
compare them using some highlighting diff tool like Emacs ediff,
tkdiff, etc.