DEFAULT_*_OPTIONS cause inconsistencies in FormHelper

For example, DEFAULT_FIELD_OPTIONS is {'size' => 30}, which causes
text_field to emit a size="30" HTML attribute. The inconsistencies are
in the RDoc; e.g., the 2nd and 3rd examples in texxt_field's RDoc are
wrong in relation to FormTagHelper, which doesn't use these defaults;
for example, un-styled text fields generated with text_field look
different from those generated with text_field_tag

I would also argue that these defaults violate the principle of least
surprise. They're also bad design practice, because they put
presentation details in mark-up. Width and height should be specified
via CSS.

I'll be happy to produce a patch that eliminates these defaults, if
there's a decent chance that it would be accepted.