Fix String#scan argument

* Add String. Not only Regexp.
* Fix description when block given(looks same as String#gsub)
Fix {Regxp,String}#match

* Adjust String#match API summary
* Write with block API for 1.9.1 and later
Fix Hash setter with String key

* Update exception class
* Narrow duplicating case (related ruby/ruby#382)
Fix a return value of Comparable#==
remove Range#equal? (closes gh-39)
Merge pull request #36 from kachick/hash-store-with_string_key

Fix Hash setter with String key
Merge pull request #35 from kachick/fix-string-scan,match

Fix String#scan and {Regexp,String}#match
add error methods
update ostruct
update Pathname#find
hide CSV.dump and load since 2.0.0
add #to_s or #inspect to Bignum, Fixnum, Float, TrueClass, FalseClass and Module
Merge pull request #38 from nkhryo/fix-comparable-double-equals

Fix a return value of Comparable#==