Rewrote `rst` mode from scratch

The old mode was not supporting many rST constructs, or not in
sufficient detail. Features/changes:

 * no `backUp` ops to keep things fast;
 * kept `python` inner mode integration;
 * added `latex` inner mode;
 * eliminated `verbatim` configuration parameter;
 * eliminated non-standard tokens: the old mode was producing `footnote`
   and `citation` tokens, which were replaced with `quote`;
 * many more details: visually compare highlighting between old and new
   to get an impression;
 * MIT license (copied and adapted form `python` mode);
minor
merge
Fixes w.r.t travis-ci.org builds

In build travis-ci.org/marijnh/CodeMirror/builds/5063554 the build
system complained about:

    * rst.js: Unused argument options (1:53)
    * rst.js: Unused var rx_SEPA (36:8)
    * rst.js: Unused var rx_NAME_WWS (43:8)
    * rst.js: Unused var rx_REF_NAME (45:8)
    * rst.js: Unused var rx_TEXT1 (48:8)
    * rst.js: Unused argument state (535:33)

Should be fixed now (all warnings).
Merge branch 'webed-rst' into webed