Dont render blank blocks

[fw42]

Very similar to #217. This one also has lots of tests. We should coordinate better :-)

@hornairs, @boourns, @csfrancis, @camilo, @dylanahsmith, @arthurnn

[fw42]

Added a few more tests/cases. Reading the tests is the easiest way to understand what effect this is going to have I think. I'm sure I forgot something. Somebody (other than me) should take a look :-)

[csfrancis]

Here are benchmarks from my machine for this branch:

[scottifyBookPro] liquid (master) $ rake benchmark:run
/opt/boxen/rbenv/versions/1.9.3-p385-perf/bin/ruby ./performance/benchmark.rb
Rehearsal ------------------------------------------------
parse:         3.160000   0.050000   3.210000 (  3.210458)
parse & run:   7.110000   0.060000   7.170000 (  7.169069)
-------------------------------------- total: 10.380000sec

                   user     system      total        real
parse:         3.150000   0.030000   3.180000 (  3.185234)
parse & run:   6.940000   0.030000   6.970000 (  6.966688)
[scottifyBookPro] liquid (master) $ rake benchmark:run
/opt/boxen/rbenv/versions/1.9.3-p385-perf/bin/ruby ./performance/benchmark.rb
Rehearsal ------------------------------------------------
parse:         3.030000   0.050000   3.080000 (  3.084493)
parse & run:   6.980000   0.060000   7.040000 (  7.037003)
-------------------------------------- total: 10.120000sec

                   user     system      total        real
parse:         3.020000   0.000000   3.020000 (  3.023140)
parse & run:   6.920000   0.040000   6.960000 (  6.958436)
[scottifyBookPro] liquid (master) $ git checkout dont_render_blank_blocks
Switched to branch 'dont_render_blank_blocks'
[scottifyBookPro] liquid (dont_render_blank_blocks) $ rake benchmark:run
/opt/boxen/rbenv/versions/1.9.3-p385-perf/bin/ruby ./performance/benchmark.rb
Rehearsal ------------------------------------------------
parse:         3.170000   0.050000   3.220000 (  3.222177)
parse & run:   7.180000   0.030000   7.210000 (  7.200545)
-------------------------------------- total: 10.430000sec

                   user     system      total        real
parse:         3.130000   0.020000   3.150000 (  3.146572)
parse & run:   7.080000   0.020000   7.100000 (  7.101301)
[scottifyBookPro] liquid (dont_render_blank_blocks) $ rake benchmark:run
/opt/boxen/rbenv/versions/1.9.3-p385-perf/bin/ruby ./performance/benchmark.rb
Rehearsal ------------------------------------------------
parse:         3.070000   0.040000   3.110000 (  3.114575)
parse & run:   7.000000   0.030000   7.030000 (  7.026592)
-------------------------------------- total: 10.140000sec

                   user     system      total        real
parse:         3.050000   0.010000   3.060000 (  3.061203)
parse & run:   6.960000   0.040000   7.000000 (  6.995924)

Results are similar to #217 (comment)

[tobi]

I think that's a nice solution.