Merge tag '0.15' into develop

v0.15
Removed extra newline
Bugfix. Use right key for mapping
Removed unused imports
Bugfix. Fixed typo and add missing import
Use correct error
Fixed typo in docstring
Bugfix. Add missing self param
Bugfix. Corrected use of is_stopped
PEP8 alignment
Doc changes
Removed newline
Refactor operators to C# like extensionmethods
Merge
Updated readme
Started adding BlockingObservable
Docstring and comment changes
Fixed typo
Fixes and tests for for_each()
Fixed docstring