Made sure the correct analyzer is used for parsing metadata queries.
Added the usecontent parameter to select the concordance type.

usecontent=orig will use the original XML content to make concordances,
which is slower but more accurate than the default (using the forward
index, which e.g. gets rid of inline tags).
Made usecontent parameter work for snippet operation as well.
Fixed exception when specifying a non-existent document id.
Accessed Concordance fields through methods instead of directly.

The left, hit and right fields have been deprecated and will be removed
in the future. Their values are calculated dynamically now.
Made it possible to fetch and highlight parts of documents.

Both the snippet operation and the contents operation now have
parameters to fetch a specific chunk of the document: wordstart and
wordend. Pass -1 to indicate start/end of the document. The part of the
document will be made well-formed automatically if necessary.
Highlighting works as normal.