Merge branch 'v1.8.x' of github.com:rethinkdb/rethinkdb into v1.8.x
Delete a single element in the history. Related to #1297
Adds pattern matching filter.
Adds tests for pattern matching filter.
Add docs for cursor.close
Fix link for the website
Made comments more grammary.
Moved func_cache_t out of env_t.
Moved global_optargs_t out of env_t.
Separated gensym_t out from env_t.
Moved scopes_t out of env_t.
Moved implicit_vars_t out of env_t.
Moved cluster_env_t out of env_t.
Gave throw_if_interruptor_pulsed a friendly  THROWS_ONLY declaration.
Made env_t::this_machine be const.
Made ql::sym_t exist and be used for gensym values.
Added missing sym.hpp and sym.cc files from previous commit, removed env_t::gensym.
Removed unused func_t::js_runner variable.
Made RSI comments more polite and removed the unused functions ql::pb::{set_int,set_str}.
Adds literal syntax to filter.