Ignore specified labels & other features

I added some features:

- partial evalb prm file support:
  - parameter DELETE_LABEL is supported so that
    root & punctuation can be ignored.
  - parameter LABELED or option -u can be used to do
     unlabeled evaluation; made into option to avoid duplicate code.
- support lemma field of export format
- use (multi)set operations
- add exact match
- read everything as UTF-8 unless otherwise specified
- require python 2.7+ and support python 3.3+

Todos:

- length limit (CUTOFF_LEN)
- add POS tag accuracy
- suggestion: change name to evaldisc, or evaldb (=evaluate discontinuous bracketings), because the script is not directly related to LCFRS, as DPSG or Hall & Nivre's model could also be evaluated with it.
- PyPI release (related to name change, as '-' is discouraged in package/module names)