kgio 2.0.0 - major internal API changes

(no code changes from 2.0.0pre1)

This release should make Kgio easier and more consistent
to use across a variety of libraries/applications.

The global Kgio.wait_*able(=) accessor methods are gone in favor
of having default kgio_wait_readable and kgio_wait_writable
methods added to all Kgio-using classes.  Sub-classes may (and
are encouraged to) redefine these if needed.

Eric Wong (7):
    expand Kgio::*#kgio_read! documentation
    prefer symbolic names for waiting read/writability
    EOFError message matches Ruby's
    README: Gemcutter => RubyGems.org
    update documentation with mailing list info
    add default kgio_wait_*able methods
    switch entirely to kgio_wait_*able methods