Improve readme.

Changed main heading, added contents, FAQ, and press, and fixed various minor issues.
Improve a hyperlink in readme.
Improve readme.
Update readme.

Added an item about making a Latin version of the app to the FAQ.
Update SDK and build tools and fix errors.

- Updated SDK to version 21.
- Updated build tools to version 21.
- Updated Android gradle plug-in to version 0.13.2.
- Updated Gradle wrapper to use Gradle version 2.1.
- Fixed several errors reported by linter.
Merge branch 'dev' of github.com:blinskey/greek-reference into dev
Make debug builds unsigned.
Fix a layout bug.

Replaced "wrap_content" attributes with "match_parent."
Improve compatibility with SDK versions < 17.

Added android:paddingRight attribute to
greek_simple_list_item_activated_1.xml.
Modify .gitignore.

Ignore top-level "build" directory.
Add Material Design theme.
Update readme and manifest for v1.5.0.