fix a few typos in the manual
support left recursive rules with potential performance hit

As described in

  Alessandro Warth, James R. Douglass, Todd Millstein, 2008,
  "Packrat Parsers Can Support Left Recursion".
  http://www.vpri.org/pdf/tr2007002_packrat.pdf

* WITH-CACHED-RESULT detects left recursion and (unless signaling an
  error has been requested) handles the situation by growing a "seed
  parse" via repeated application of the rules involved in the left
  recursion.

* The new special variable *ERROR-ON-LEFT-RECURSION* switches between
  this new behavior and the old behavior of signaling a LEFT-RECURSION
  error.

* The system version has been bumped from 0.9 to 0.10 and a feature
  :ESRAP.CAN-HANDLE-LEFT-RECURSION is pushed onto *FEATURES* when the
  system is loaded.

* Basic unit tests for direct and indirect left recursion have been
  added: LEFT-RECURSION.[IN]DIRECT.{SUCCESS, CONDITION}.

* The manual and README have been extended.

* The new file example-left-recursion.lisp contains multiple grammars
  which exercise and illustrate the new capability.