Textcomplexity

- Add measures of volume, i.e. text length, to
`textcomplexity.surface`. Default measures: Log10 of text length
in tokens (`--preset core`) and log10 of text length in characters
(`--preset all`).

- Add dispersion measures (Gini-based dispersion and evenness-based
dispersion).
- Add pos-based measures (lexical density, rarity).
- Add Jarvis's (2013) evenness (standard deviation of tokens per
type).
- Language-specific information can be provided via language
definition files (`--lang-def`); already built-in for German and
English (simply specify `--lang de` or `--lang en`).
- New presets of measures (lexical\_core, core, extended\_core, all);
ignore measures that are not applicable.
- New option `--ignore-case`.
- Update documentation.
- Improve warning about window size.

- Bugfix: Use 0.172 instead of -0.172 as default value for alpha in
Brunet’s W.
- Bugfix in code for reading custom tsv format.

- Initial release.