Support fragments

[i-like-robots]

Fixes #9

The change seems to have had a small impact on benchmarks:

Benchmark run on Thu 19 Apr 2018 11:26:22 BST with Node v8.9.4

hyperapp@1.2.5
Requests per second:    2826.85 [#/sec] (mean)

hyperons@0.3.0
Requests per second:    3232.55 [#/sec] (mean)

inferno@5.0.4
Requests per second:    2873.06 [#/sec] (mean)

nerv@0.3.0
Requests per second:    2329.46 [#/sec] (mean)

preact@8.2.7
Requests per second:    2439.88 [#/sec] (mean)

rax@0.6.0
Requests per second:    3377.05 [#/sec] (mean)

react@16.3.2
Requests per second:    2264.95 [#/sec] (mean)

[coveralls]

Coverage decreased (-2.7%) to 95.89% when pulling 023e9ee on support-fragments into 8bb162d on master.