Remove Bluecloth as default markdown processor

[lsegal]

Bluecloth 2.0.11 has bugs processing a_b c_d scenarios. There have also been a number of other issues, and growing support for other libraries. This ticket discusses the other possible markdown libraries that can be made default for YARD.

Other libraries:

• kramdown - pure Ruby
• rdiscount - native

Ideally YARD would have a pure Ruby implementation, though we must also consider performance issues and use native code if it is significantly faster. The benchmarks shown by kramdown illustrate that it is ~50x slower than bluecloth. RDiscount is only 1.1x slower. We should still look at the benchmarks of actual YARD templates to see how this affects real speed.

Right now it looks like rdiscount would be a better choice, benchmarks pending.

[postmodern]

Yes please.

RDiscount is the better choice for MRI and Rubinius. However, it cannot be installed on JRuby <= 1.5.x.

Kramdown is decently "fast" and can be used on all Ruby implementations.

[lsegal]

Keep in mind that this is just the "default". For a system without access to rdiscount, the next in the list would be used. We could use a native as the default and drop down to the pure ruby kramdown for those who are unable to install rdiscount.

But I'm still interested to see the actual performance increase that rdiscount really has in a yardoc run.

[lsegal]

Preliminary results (parsing YARD's own source):

yard (master)$ time ./bin/yardoc -m markdown -M bluecloth -q

real    0m15.390s
user    0m14.648s
sys 0m0.688s

yard (master)$ time ./bin/yardoc -m markdown -M rdiscount -q

real    0m15.150s
user    0m14.493s
sys 0m0.665s

yard (master)$ time ./bin/yardoc -m markdown -M kramdown -q

real    0m25.880s
user    0m24.915s
sys 0m0.873s

The current order for markdown providers is: bluecloth, kramdown, maruku, rpeg-markdown, rdiscount

I would suggest the following new order:

rdiscount, kramdown, bluecloth, maruku, rpeg-markdown