Release version 0.1.3: Maven Central ready, new {@.file.textlet} features

New release: version 0.1.3

Notes:
- Changed codelet-*-core.jar to codelet-*.jar
- Now has a POM for both deploying jars to Maven Central, and so other
projects can use Codelet via Maven Central.
- {@.file.textlet} (see
com/github/aliteralmind/codelet/CodeletType.html#FILE_TEXT):
- ADDED: Ability to prefix path with an environment variable or system
property. Example: "$/subdir/input.txt"). Idea from Stack Overflow user
Unihedron.
- ADDED/CHANGED: Relative paths containing single url slashes ('/') as
its file separator, are automatically changed to the appropriate
separator for the underlying OS. Absolute paths are unaltered.