Merge pull request #127 from devoncarew/update_ci

Update the CI configuration; add markdown badges

null safety stable release (#109)

Fix registerCustomWatcher to allow nulls (#107)

The idea behind the closures passed to `registerCustomWatcher` is that
they should return `null` if the particular implementation does not
support the provided path (in which case we should fallback to other
implementations).

Modified a test to check this.

Prepare to publish (#89)

Prepare to publish, tighten pub constraints (#81)

- Add a changelog entry.
- Remove unused author key from pubspec.
- Tighten the constraints on dependencies for any which had a lower
  major version bound than the package versions which support Dart 2.

Update .gitignore (#77)

Prepare to publish 0.9.7+12 (#72)

Catch FileSystemException during existsSync() on Windows. (#67)