This commit adds support for formatting markdown files with "deno fmt".
Additionally "--ext={js|jsx|ts|tsx|md}" flag was added to "deno fmt"
that allows to specify file type when providing contents over stdio.
This commit adds support for "--watch" flag for "bundle"
and "fmt" subcommands.
In addition to this, it refactors "run --watch" command so that
module resolution will occur every time the file watcher detects
file addition/deletion, which allows the watcher to observe a file
that is newly added to the dependency as well.
This commit renames "fs" module in "cli/" to "fs_util". This is purely
cosmetic change; there were a few places which aliased "crate::fs"
to "deno_fs" which was very confusing with "fs" module in ops.
