Adds pattern matching filter.
Adds tests for pattern matching filter.
Add docs for cursor.close
Fix link for the website
Adds literal syntax to filter.
Adds tests for literal fitler syntax.
Adds docs on pattern matching filter.
Added unused var_visibility_t and var_scope_t types.
Moved bounded_op_term_t constructor implementation to op.cc.
Made bounded_op_term_t not evaluate its optargs at construction time.
Merge branch 'next' into merge_br
Merge branch 'next' into sam_1328 (nested filter_call changes)

Conflicts:
	src/rdb_protocol/func.cc
	src/rdb_protocol/terms/seq.cc
Made us not compute default_filter_val until the eval_impl in filter_term_t.
make python driver install backup scripts

rather than cycle through multiple potential python binaries with which
to run a script hoping to find the appropriate package, it makes much
more sense to install the scripts with their dependency into the
location of the python binary with which the package was installed.

this pegs the #! to the version of python used to install (whether
system version or venv) and allows the script to run in the appropriate
environment.
Remove references to the backup scripts
Merge 1355 into next

Review 893 by @tryneus
Closes #1355
Merge branch 'next' into sam_1328
Moved func_t::new_*_func static functions outside of func_t.
Revert "Made us not compute default_filter_val until the eval_impl in filter_term_t."

This reverts commit e6a0f3c9bbc9acb56542f190dec28128eba05de9.

It also fixes a really surprising polyglot test failure.  Our code is
completely insane fragile crap.
Made func_t an abstract class, with one subclass (concrete_func_t, whose implementation is not substantially changed).