Pedl

New features:
- `predict` now accepts HGNC symbols
- `summarize` now reports the maximum score of all sentences for each association
- `summarize` now allows to aggregate information per protein pair, regardless of association type and direction

Bug fixes:
- Fix massive memory consumption
- Fix incompatible dependencies between lxml and bioc

This release splits PEDL's functionality into `pedl predict` and `pedl summarize`.

`predict` receives a new option `--skip_reverse` which omits the prediction from `p2` to `p1`, which can be useful when the lists for `p1` and `p2` are the same.

- Stop progress bars from cluttering the terminal
- Handle errors in requests to PubTator API
- Do not create empty files for pairs without any detected relation

This is the first release of PEDL. The project is in an alpha state. It should be usable, but it is not ready for production.