Fixed some more integer cast warnings on iOS

Public issue #106

Public issue #106

This may be changed to a general config property later.

Related to public issue #119

Jack back-end ignores midi ports

Add defined(MA_APPLE_MOBILE) guard around AVAudioSessionCategory code

Public issue #101

  * The session category can now be configured via the context config. When
    set to ma_ios_session_category_default, it will try PlayAndRecord,
    Playback and Record (in that order) until one works. If none work it
    leave the category untouched. This will also set the DefaultToSpeaker
    option since in most cases an application will want audio to be emitted
    from the speaker rather than the receiver.  If the application does not
    want to change the session category, use ma_ios_session_category_none.

  * The session category options can now be configured via the context
    config. This maps to the AVAudioSessionCategoryOption flags.

Public issues #101, #113

Public issue #108

Public issue #110

Public issue #110

Public issue #110

Public issue #114.

This will be replaced with a more complete solution later.

Public issue #105.