Dctap

- Tweaked terminology used in glossary following discussion in DCTAP WG.

- Improved documentation.

- Added support and documentation for value constraint types MinLength and MinInclusive.

[Unreleased]

- Added improvements to README.rst.

- Added examples section to default help display when command run without arguments.
- Added CHANGELOG.md.

- Added examples and explanation to Readthedocs.
- Fixed so that "extra" elements passed through to output with original upper/lowercase.
- Added (optional) warnings to stderr not just for text output, but for JSON and YAML.
- Added (optional) warning when header not recognized as DCTAP element or a configured extra.