Update `nGram` and `treebankTokenize` functions.
Update `nGram` and `treebankTokenize` functions.

Changes to `nGram`:
- Fix error in merging configuration options caused by incorrect use of default parameters
- Fix unintentional mutation of the token array when applying padding on either side
- Fix incorrect indexing when iterating through the array causing the last gram to be omitted

Changes to `treebankTokenize`:
- Add spacing around '``' when replacing opening quotes. Without this, opening quotes are not tokenized.
- Add support for em-dashes (or arbitrary length dashes)
- Add support for arbitrary length ellipses
- Add support for tokenized EOL commas

kenlimmj/rouge