Release 3.14.0 of the Checker Framework

[Suzanne Millstein]

We have released a new version of the Checker Framework.
The Checker Framework lets you create and/or run pluggable type checkers, in order to detect and prevent bugs in your code.

You can find documentation and download links at:
http://CheckerFramework.org/

Changes for Checker Framework version 3.14.0

**User-visible changes:**

The Units Checker supports new qualifiers (thanks to Rene Kraneis):
 * `@Volume`, `@m3`, `@mm3`, `@km3`
 * `@Force`, `@N`, `@kN`
 * `@t` (metric ton, a unit of mass)

Stub files can now override declaration annotations in the annotated JDK. Previously, stub files only overrode type annotations in the annotated JDK.

Command-line argument `-AstubWarnIfNotFound` is treated as true for stub files provided on the command line.

**Implementation details:**

Method `SourceChecker.getProperties` takes a third formal parameter `permitNonExisting`.

Method `TreeUtils.getMethodName()` returns a `String` rather than a `Name`.

Removed CheckerDevelMain.

**Closed issues:**
#3993, #4116, #4586, #4598, #4612, #4614.