Export watch_file.

Export watch_file, as this is the easiest API entry point between FileMonitor
and PollingFileMonitor.

Fix _uv_hook_fseventscb such that the condition is notified even if no callback
is in the monitor. Also fix the value sent to notify() to match the expected
return value in wait().

Fix watch_poll default callback.
Document watch_file method.
Add a test for wait(FileMonitor).
Unexport new UV_ constants.
WIP: File watching event refactor.
Re-passing tests.
fix a couple potential bugs handling method definitions of qualified names (a.b)
Updated darray and @paralle to reflect usage of only worker processes.
some performance tweaks to the parser
front-end optimization: faster "quote" for subexpressions not containing $

this avoids building and evaluating big expressions that build expressions,
instead using the expr to build as data and simply copying it.
shaves 10-15% off sysimg build and other code loading, especially where
big macros are used.
Merge pull request #4255 from amitmurthy/amitm/docupd

Doc: Updated darray and @parallel to reflect usage of only worker processes.
Update linalg.rst

missing ` in documentation for "repeat".
Merge pull request #4257 from sje30/patch-1

Update linalg.rst
Refactor events with integer flag fields and accessors.
Fix logic bug in FDWatcher wait()
Disable shift-invert arpack tests.
Pkg.status: more informative output (unregistered, dirty attributes)
Pkg.tag: ensure that existing has eltype VersionNumber.

This could cause no method errors in certain circumstances.
Pkg.tag: allow symbolic versions defaulting to :patch [close #4092]

Also refuse to tag when the package repo is dirty. This is to keep
people from accidentally tagging without committing everything. If
you really have changes that you don't want to include in the tag
then you can just stash them while tagging.
Pkg.tag: distinguish between bumping (default) and patching.

Bumping the version will remain on 0.0.0 (or other rewritable versions)
whereas patching will always go to the next real patch version.