Allow requesting try_lint() to only run linters supporting stdin (#907)

* Allow filtering linters to be run by try_lint()

When hooking linting to an event like InsertLeave, running linters that
only work with content that already made to the storage does not make
sense.

Enhance try_lint() to accept an optional filter function in its
set of options. When this option is present only linters for which it
returns "true" will be run.

try_lint() will also accept a shorthand "stdin" string in place of
the filter function, in which case try_lint() will skip all linters that
do not advertise stdin support (via linter.stdin).


Co-authored-by: Mathias Fussenegger <f.mathias@zignar.net>