Release procedure

Preliminaries

Make sure that you are in master branch:
```
git checkout master
```
Make sure that RELEASE_NOTES.rst and ANNOUNCE.rst are up to date with the latest news in the release.
Check that VERSION symbols in caterva/caterva.h contains the correct info.

Commit the changes with:

git commit -a -m "Getting ready for release X.Y.Z"

Create a new build/ directory, change into it and issue:

cmake ..
cmake --build .
ctest

Make sure the documentation is rendering well:

cd docs/sphinx
make html
open _build/html/index.html

Create a tag X.Y.Z from master. Use the next message:
```
git tag -a vX.Y.Z -m "Tagging version X.Y.Z"
```
Push the tag to the github repo:
```
git push
git push --tags
```
Add the release notes for this tag in the releases tab of github project at: https://github.com/Blosc/Caterva/releases

Send an announcement to the blosc list. Use the ANNOUNCE.md file as skeleton (possibly as the definitive version).
Tweet about this from the @Blosc2 account and rejoice!

Edit VERSION symbols in caterva/caterva.h in master to increment the version to the next minor one (i.e. X.Y.Z --> X.Y.(Z+1)-dev).
Create new headers for adding new features in RELEASE_NOTES.md and add this place-holder instead:

XXX version-specific blurb XXX
Commit the changes:

git commit -a -m "Post X.Y.Z release actions done" git push

That's all folks!