Data Bindings in CsoundObj

After much discussion with Steven Yi, I have used his renaming suggestion and updated the API to rename the objects that bind external objects to Csound from the somewhat confusing "CsoundValueCacheable" to "CsoundDataBinding".  The valueCache internal to Csound remains unchanged.  I've updated the CHANGELOG and the Csound Manual in TeX.  I've cleaned up the code around the current data bindings, and added new classes for labels: CsoundLabelBinding, and momentary and non-momentary buttons (CsoundMomentaryButtonBinding) and CsoundButtonBinding).  All of the examples have been updated to use the new nomenclature.  The examples SimpleTest1 and SimpleTest2 now demonstrate use of CsoundLabelBinding.  The button example uses momentary button because a regular button (1=down, 0=up) resulted in overloading Csound with i events.  I committed each change with considerable granularity so the commit log shows the finer scale of small fixes that were also made along the way such as renaming ControlRectangle.  Even if the name CsoundDataBinding were to be replaced, this pull request contains a lot of good improvements and a simple name change would be a relatively minor update.  These changes will also appear in Csound for OSX in a separate branch that will be pull requested after this merge.