Begin rewrite of indentation code

The objectives are:

    1. Simplify the indentation code; previous implementation has become
       so complex it is impossible to maintain,

    2. Significantly improve performance; previous indentation code was
       painfully slow, (see issue #6)

    3. Maximum configurability; should be configured similarly to cljfmt
       and make previously impossible things possible (e.g. issue #21).

As of this commit, objectives 1 and 2 have been met, but work on
objective 3 has not yet begun.  There will continue to be further
improvements, particularly around performance and the "what if syntax
highlighting is disabled?" scenario.

These changes will unfortunately be backwards incompatible, but
hopefully the improved performance and API will make up for it.