work with browserify easily
Allow merging (Multi)Point geometries
Simplify each arc separately.

Rather than build one large heap for all arcs, we build a heap for each
arc separately and simplify one arc at a time.  A quick benchmark using
Natural Earth’s 10m admin-0 data simplified at 1e-5 results in a 2x
speedup with this change.  This is due to reduced peak memory usage and
faster heap operations on the smaller heaps.
Update to rw 0.1.
Slightly cleaner.
Merge branch 'browserify' of github.com:calvinmetcalf/topojson into browserify
Merge branch 'merge-points' into 1.6.15
Merge branch 'rw' into 1.6.15
Merge branch 'simplify' into 1.6.15
Merge branch '1.6.15'