[DOCS] updated json responses after #4310 and #4480

 - Removed "ok": true from response examples
 - Added "created" flag to index response examples
 - Replaced exists flag with found in delete response examples
[DOCS] Tidied up asciidoc for migration page
[SPEC] Added human flag to:
* cluster.node_info
* cluster.node_stats
* indices.segments
* indices.stats
* indices.status
[DOCS] Fixed typo in frontends.asciidoc
[SPEC] Added the routing and timeout params to bulk
[SPEC] Added cat.json
[SPEC] Added cluster.repositories.* and cluster.snapshots.*
[SPEC] Added cluster.stats.json
[SPEC] Added cluster.pending_tasks.json
[SPEC] Added version, version_type to get and get_source
[SPEC] Added _source, _source_include, _source_exclude to get_source
[SPEC] Removed percolate from index.json
[SPEC] Added timeout, master_timeout to cluster.get_settings and cluster.reroute
[SPEC] Removed percolate from update
[SPEC] Added empty path to indices.open and indices.close
[SPEC] Removed refresh from indices.flush and indices.optimize
[SPEC] Added force to indices.refresh
[SPEC] Added local to indices.get_mapping and indices.get_field_mapping
[SPEC] Added indices.exists_template.json
[SPEC] Fixed bad JSON in indices.open