avoid inlining methods in Form class for readability
clean up whitespace for method argument defaults
avoid using "new" as a variable name on select_list
added optional options hash to `File#save`

Include an `:overwrite` option which overwrites the original
saved file when true, otherwise falls back to the default
behaviour of appending numbers to the filename

closes #219
updated changelog for #219
added more docs and an example for File#save
Merge branch 'master' of github.com:sparklemotion/mechanize