SymCalc Ruby 1.0.1

Release of SymCalc Ruby 1.0.1

Description
This patch addresses the following issues:

• Issue #1: As suggested by @xxx, SymCalc::Division#__derivative__ now forwards the variable argument
• Issue (undocumented): Instance methods now use SymCalc.to_equation instead of to_equation, fixing the 'undefined method 'to_equation'' error if SymCalc wasn't included.

Changelog
v1.0.0 to v1.0.1