bson: allow dot keys in bson_has_field().

You can now perform the following:

  bson_has_field (b, "foo.0.bar");
doc: start on new mallard based docs.
build: fixup automake for new docs.
build: print configuration result.
doc: xlink json
git: ignore html dir.
doc: add documentation on installing libbson.
doc: add oid docs.
doc: add subtitle.
doc: start on streaming bson examnple.
doc: add writer example.
doc: add performance notes for string building.
doc: update subtitle.
examples: use stack allocated bson for json-to-bson.
doc: add section on streaming json parser.
doc: add section on error handling.
doc: add docs for bson_context_t.
doc: add bson_error_t docs.
doc: add bson_iter_t docs.
doc: add bson_json_reader_t doc.