Resolve "release v1.2.0"

Closes #257 (closed)

CHANGELOG.md

 # Changelog
 All notable changes to this project will be documented in this file.
 
+## v1.2.0 -  2020-12-18  - parallel preprocessing and improved data handlers
+
+### general:
+
+ * new plots
+ * parallelism for faster preprocessing
+ * improved data handler with mixed sampling types
+ * enhanced test coverage
+ 
+### new features:
+
+* station map plot highlights now subsets on the map and displays number of stations for each subset (#227, #231)
+* two new data availability plots `PlotAvailabilityHistogram` (#191, #192, #223)
+* introduced parallel code in preprocessing if system supports parallelism (#164, #224, #225)
+* data handler `DataHandlerMixedSampling` (and inheritances) supports an offset parameter to end inputs at a different time than 00 hours (#220)
+* args for data handler `DataHandlerMixedSampling` (and inheritances) that differ for input and target can now be parsed as tuple (#229)
+
+### technical:
+
+* added templates for release and bug issues (#189)
+* improved test coverage (#236, #238, #239, #240, #241, #242, #243, #244, #245)
+* station map plot includes now number of stations for each subset (#231)
+* postprocessing plots are encapsulated in try except statements (#107)
+* updated git settings (#213)
+* bug fix for data handler (#235)
+* reordering and bug fix for preprocessing reporting (#207, #232)
+* bug fix for outdated system path style (#226)
+* new plots are included in default plot list (#211)
+* `helpers/join` connection to ToarDB (e.g. used by DefaultDataHandler) reports now which variable could not be loaded (#222)
+* plot `PlotBootstrapSkillScore` can now additionally highlight specific variables, but not included in postprocessing up to now (#201)
+* data handler `DataHandlerMixedSampling` has now a reduced data loading (#221)
+
 ## v1.1.0 -  2020-11-18  - hourly resolution support and new data handlers
 
 ### general: