Misc enhancements and few fixes.

Fixes:
+ Use buffer size of 65535 to be always safe.
+ Check against possible DOS (part size of 0).
+ More checks of decode errors.

Enh:
+ Use own expection on decode errors.
+ Simpler decode functions.
+ asserts on module top level.
+ Separated Reader to a Parser class.
+ Possibility to subclass/extend Values or Notification.

+ Added tests !
Merge pull request #2 from gst/misc_enhancements_v1

Misc enhancements and few fixes.