Merge char improvements, doc changes, version 1.1.9 (ikalchev#79)

* Remove breaking change description from README.

* Characteristic improvements (ikalchev#73)

* Merged set_value and get_hap_value

* Small improvements
* Added helper method '_validate_value'
* Added helper method '_get_default_value'
* Raise ValueError if properties are invalid
* Added __slots__

* Additional changes

* New method: update_value (use for value updates from HAP-python)
* Rename: to_HAP to to_dict
* New method: from_dict (use during loading of chars)

* Addressed comments

* Fixed errors, small mistakes

* Added debug statements

* Changed '_LOGGER' to 'logger'

* Changed raise error to return None

* Raising ValueErrors with custom msg

* Bugfix, added additional logger.error statements

* Rearanged functions

* Added error_msg parameter

* Added tests

* Added '/htmlcov' to .gitignore

* Bump version number to 1.1.9

Merge pull request ikalchev#56 from cdce8p/representations

Added object representations