Allow multiline values for :as in options via customized :summary-fn

[lread]

The value for :as acts as an option's description. Like the :app and :command
:description, :as now optionally supports multiline text via a vector of
strings.

Notes:
Cli-matic takes advantage of clojure.tools.cli to format options for display
in help. Ideally clojure.tools.cli would accept multiline descriptions for
options, but it does not.

We take advantage of clojure.tools.cli's :summary-fn to override default
handling and support multilines.

This work includes the strengthening of the spec for descriptions. A description
must be a non-blank string - or - a collection of strings that includes at least
one non-blank string.

I also moved the beef of get-clojure-options under utils to localize
interactions with clojure.tools.cli

Fixes #94

[lread]

I think this might be a better approach than #95, but each has its pros and cons.

#95

• pros
  • is probably a bit simpler to grok
• cons
  • definitely more of a hack
  • could suffer text marker collision (although we could overcome that possibility if you prefer Allow multiline values for :as in options. #95).

#96

• pros
  • is cleaner
  • will handle expanding and aligning any multiline text found in options
  • will suffer no marker collisions
• cons
  • maybe a bit more complicated
  • touches clojure.tools.cli internals which were formerly a black box for cli-matic.

These 2 PRs do share some common changes, to see what is different between them here's comparison of 95 vs 95.

I'll let you decide which to merge and which to reject.

[lread]

Hi @l3nz, is there anything more you'd like me to do on this?

An alternative would be to propose a change to https://github.com/clojure/tools.cli itself. I expect the specification of multiline values as vectors would remain in the domain of cli-matic, but clojure.tools.cli could be altered to handle newlines in options.