More tests
Put RootIO.t and Tempfile.t tests into IO.t since they all test Bio::Root::IO

+ some test updates
POD updates and tabulation
Improved mode() method

The previous code failed and reported 'w' for files that had been read entirely
(<$fh> returned undef). Also, it did not save the mode() determined from non-
filehandles, '?'.

The new approach to determine if a stream is readable or writable is to read or
write 0 characters to or from it and check return status to find out if that
was successful.

+ some general code tabulation fixes, cleanups, POD clarifications
Return true on close() success

+ some tabulation fixes
POD changes and more tests
mode() supports streams in 'rw', read+write mode
Updated Changes file