Prepare for the release (changelog, README, copyright, etc)

[alexamici]

Add changelog entries for several older issues:

• closes Cannot import cfgrib if ecCodes is not present on the system. #14
• closes Drop internal ecCodes bindings and switch to eccodes-python #95
• closes pyeccodes is not API compatible with eccodes. #204
• closes Problem installing cfgrib via conda - module 'pyeccodes.compat' has no attribute #147
• closes Review thread-safety of the way we access ecCodes #141
• closes Speed up of Cfmessage #197
• closes Add a "dump" command to cfgrib #50

[codecov-io]

Codecov Report

Merging #221 (8d8904e) into master (919a513) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #221   +/-   ##
=======================================
  Coverage   92.29%   92.29%           
=======================================
  Files          25       25           
  Lines        1714     1714           
  Branches      201      201           
=======================================
  Hits         1582     1582           
  Misses        110      110           
  Partials       22       22           

Impacted Files	Coverage Δ
cf2cdm/__init__.py	100.00% <ø> (ø)
cf2cdm/cfcoords.py	100.00% <ø> (ø)
cf2cdm/cfunits.py	100.00% <ø> (ø)
cf2cdm/datamodels.py	100.00% <ø> (ø)
cfgrib/__init__.py	100.00% <ø> (ø)
cfgrib/__main__.py	93.33% <ø> (ø)
cfgrib/cfmessage.py	95.45% <ø> (ø)
cfgrib/dataset.py	98.93% <ø> (ø)
cfgrib/messages.py	93.77% <ø> (ø)
cfgrib/xarray_store.py	93.54% <ø> (ø)
... and 1 more

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[alexamici]

@iainrussell I'll consider this PR uncontroversial enough to merge it without your explicit approval, but I need you have a look at #220 as it is more tricky and I'll need your approval to merge and proceed with the release.