Update for accurate initialization and state management.

[mtmccrea]

Great tutorial!

These proposed changes provide fixes and comments regarding handling the state variables, as well as fix the initialization of the UGen.

Some of the more important changes include:

• making sure the initialization sample is equal to the first sample
• resetting the state of the UGen in the constructor to make sure the ramp starts at 0.
• updating a local variable phase in the calculation functions, rather than member variable m_phase
• initializing the frequency with the user-specified value (it was just 0 before, causing a ramp-up of the frequency from 0 to in0(Frequency) over the first block)
• the .schelp file was updated to more fully utilize helpdoc syntax, fill out header metadata, and provide more examples that double as examples of snippets useful for testing UGens generally (e.g. checking behavior of different input rates)

The tutorial itself has been updated to reflect these changes, and some elaboration was provided on certain topics, namely documentation, to encourage best practices.

Note: I didn't update the .pdf or .epub files, in case some changes are rejected or further changes are made in response.

[madskjeldgaard]

Fantastic stuff. Thanks so much!