CLI2: Eliminated CLI

- This is a large commit, as all the changes are centered around the elimination
  of CLI.
- CLI is no longer compiled.
- Context no longer maintains CLI + CLI2.
- Filter now walks the parse tree and sends to Eval a
  std::vector <std::pair <std::string, Lexer::Type>> containing only args tagged
  with FILTER.
- Filter more efficiently sets/unsets Eval::debug, by doing it less often.
- The filterExpr.length() check is no longer meaningful, and instead the size of
  the std::vector above is used.
- Filter::pendingOnly performs better analysis.
- Filter::safety makes use of the std::vector size also.
- Task::modify makes use of 'canonical' rather than 'name', which is a policy
  change, not a fix.

src/commands/CmdContext.cpp

@@ -144,7 +144,7 @@ int CmdContext::defineContext (std::vector <std::string>& words, std::stringstre
     try
     {
       // This result is not used, and is just to check validity.
-      context.cli.addRawFilter ("( " + value + " )");
+      context.cli2.addFilter (value);
       filter.subset (pending, filtered);
     }
     catch (std::string exception)