compat library for Opal
opal constant
replace '[:blank:]' pattern with ' \t'
replace '[:alnum:]' pattern with 'a-zA-Z0-9'
replace '[:alpha:]' pattern with 'a-zA-Z'
replace '[[:digit:]]' pattern with '\d'
Merge pull request #667 from Mogztter/opal-constant

Introduce OPAL constant to indicate whether the Ruby engine is Opal.
split opal/compat.rb into multiple files, move to opal_ext
define constants for regexp character classes
fully-qualify OPAL constant as RUBY_ENGINE_OPAL

also define a parallel constant for JRUBY
Merge pull request #1 from mojavelinux/pr-666-review

Move opal/compat.rb to opal_ext, split into multiple files
Merge pull request #2 from mojavelinux/pr-668-review

Use constants for regexp character classes
Merge pull request #666 from Mogztter/opal-compat
flatten any_list regexp to single line
Merge pull request #668 from Mogztter/opal-regexp
switch to RUBY_ENGINE_OPAL in conditional
set File::ALT_SEPARATOR in opal_ext/file
revert to Struct in cases supported by Opal
Merge pull request #675 from Mogztter/opal-struct
fix nested regex character class in Ruby 1.8