Fix Kernel.#set_trace_func

Fix example and klass parameter of proc.
Add description of ISDIGIT
Fix optparse/time example
Merge pull request #87 from mneilsen/master

Fix optparse/time example
Merge pull request #86 from utenmiki/update-ISDIGIT

Add description of ISDIGIT
add Module#singleton_class? since 2.1.0
add {exception: false} optional argument to IO#read_nonblock and #write_nonblock since 2.1.0
fix typo
fix typo
Merge pull request #89 from guemon/master

fix typo
add @see to String#split
Update IO.popen
Merge branch 'master' of github.com:rurema/doctree
Update about gem search. (closes gh-76)
Update IO.popen
Update Kernel.#spawn about file descriptors, :close_others and :close options
update links. (refs gh-90)
Merge pull request #85 from yui-knk/fix-set_trace_func

Fix Kernel.#set_trace_func
Fix typo.
Merge pull request #92 from yui-knk/fix-typo-drb

Fix typo.