Changelog for s-cargot-letbind-

Revision history for s-cargot-letbind -- 2018-03-02 -- 2018-02-16

* Added verification ability to ensure let-bind variables are
  always unique with respect to each-other and with respect to all
  generated symbol strings within the s-expression.  This is
  performed internally within the 'discoverLetBindings' function,
  but requires the ability to get the string representation of an
  S-expression atom, so the 'extractStr' function is added to the
  'DiscoveryGuide' to support this.  If not provided, or if the
  provided form returns Nothing, no validation will be performed.

* Suppress generation of let-binding phrase if there are no
  discovered bindings to apply. -- 2018-02-14

* Initial version.