Improve overall gem documentation coverage.

Minor code improvements as well.

Task 13308
Revise RDoc, formatting

Task 13308
Task 13324
Fix Sergey Potapov's rubygems.org email address

Task 13308
Task 13324
Loosen Ruby version restriction (don't restrict the patch level)

Task 13308
Task 13324
Remove redundant rspec line

Task 13308
Task 13324
Merge TMXCredit/ach_builder#7 v0.2.2 'origin/13308_improve_documentation_coverage'

Task 13308
Task 13324

note: bumped version due to minor code adjustments

* origin/13308_improve_documentation_coverage:
  Revise RDoc, formatting
  Improve overall gem documentation coverage.