Add spec to reproduce FilterPraser.parse fails with multibyte char
Simplify an example for FilterParser
Fix: Fails to parser when given string includes multibyte chars.

Net::LDAP::Filter::FilterParser fails to parse when a given string
includes multibyte chars such as Japanese characters.
But this should support it according to RFC-2254.

This commit is to fix this failure.
Merge pull request #66 from satoryu/fix_filter_parser

Bug Fix: Fails to generate filter parser when given string includes multibyte chars.