[1.8.7 Compat] Avoid using 'named captures'

Named captures are a feature of 1.9's regular expression engine and
not supported in 1.8.7.
[1.8.7 Compat] Remove use of require_relative in tests
[1.8.7 Compat] Use only Time class to avoid compatibility issues.

1.9.2 and 1.8.7 have numerous differences in the functions available
to the Time, Date, and DateTime classes.  The commit ensures that we only
use the Time class and only use methods that exist in 1.8.7.
Fix option processing for grep command.

Since the :last option has a default, it will never be nil.  Thus we
need to check :from and :to first.
Merge pull request #11 from stevendanna/issue-10

Add 1.8.7 Compatibility