Add option vector validation in compile-option-specs
Allow descriptions to be totally omitted

["-f" "--foo ARG" :default "BAR"] is now acceptable.
Clean up long-opt assertion
Add :fallback option to compile-option-specs

:default values in the opt vectors take precedence.

This allows setting the fallback default value of option vectors to a
value other than nil.

refer: https://github.com/guns/optparse-clj/issues/1
Add :fallback option to parse
Rename process-option-tokens -> parse-option-tokens
Add :pre and :post validations to compile-option-specs

:pre validates each option vector has a valid --long-opt.
:post validates the uniqueness of the resulting set of options.
Reduce indentation in reduce blocks
Move default -> desc to compile-option-specs

This allows us to hide truthy :fallback values, but also allows the user
to control what appears in the "default value" field in the summary.
Omit default column in summary when no default descs
Update documentation for :default-desc
v1.0.1