Ruby Firebird Extension Library – Fb bumped to version 0.7.1 with a few fixes

Version 0.7.1 is on RubyGems now.
With following changes and bug fixes:
Fix naive rounding logic affecting negative scaled values.
Update for current rubygems, add license MIT like ar adapter , add rakefile.
Fixes error: ‘isc_info_db_SQL_dialect’ undeclared (first use in this function) replaced in Firebird 3.0 and marked as deprecated from firebird 1.5.