introduce mrb_assert() in mruby.h
replace gc_assert with mrb_assert
replace assert with mrb_assert
if mrbc.run fail, abort rake
enabe MRB_DEBUG on travis_config.rb
refactor out longjmp() to a function
Rename --pull_gems to --pull-gems
Merge pull request #1412 from h2so5/rename-pull-gems-option

Rename --pull_gems to --pull-gems
I correct the mistakes of grammer in README.md.
I correct the mistakes of grammer in README.md. 'update' word is an countable noun.
Merge pull request #1413 from suzukaze/correct-mistake-of-grammer-in-readme.md

I correct the mistakes of grammer in README.md.
Merge pull request #1414 from suzukaze/correct-mistake-of-grammer-in-readme.md-2

I correct the mistakes of grammer in README.md.
Merge pull request #1410 from Fleurer/introduce-mrb-assert

add assert check for TravisCI
Merge branch 'master' of github.com:mruby/mruby
I replace 0 with NULL because struct pointer be should set NULL in.
replace "if not" to "unless"
I replace 'Pre-Conditions' with 'Preconditions' because the former is a wrong word.
Remove pop that was done when not a return val
Add a couple splat tests
Merge pull request #1417 from suzukaze/fix-doc-mrbgems

I replace 'Pre-Conditions' with 'Preconditions' because the former is a ...