Reorganize the documentation into separate files

Keep a "Quickstart Guide" in the README, add separate
detailed sections for development (CONTRIBUTING) and
release/deployment (RELEASE).

RELEASE.md

@@ -0,0 +1,93 @@
+# Release & Deployment Process
+
+Please read the Working Process/Quickstart Guide in README.md
+and the Development guidelines in CONTRIBUTING.md.
+
+The release process of a new version of the extension
+shall be performed by the designated *Release Manager*.
+
+Note that we expect to gradually automate more of this process.
+
+Having checked PR to be released it shall be
+merged back into the `master` branch to prepare the new release.
+
+The version number in `pg/cranckshaft.control` must first be updated.
+To do so [Semantic Versioning 2.0](http://semver.org/) is in order.
+
+Thew `NEWS.md` will be updated.
+
+We now will explain the process for the case of backwards-compatible
+releases (updating the minor or patch version numbers).
+
+TODO: document the complex case of major releases.
+
+The next command must be executed to produce the main installation
+script for the new release, `release/cranckshaft--X.Y.Z.sql` and
+also to copy the python package to `release/python/X.Y.Z/crankshaft`.
+
+```
+make release
+```
+
+Then, the release manager shall produce upgrade and downgrade scripts
+to migrate to/from the previous release. In the case of minor/patch
+releases this simply consist in extracting the functions that have changed
+and placing them in the proper `release/cranckshaft--X.Y.Z--A.B.C.sql`
+file.
+
+The new release can be deployed for staging/smoke tests with this command:
+
+```
+sudo make deploy
+```
+
+This will copy the current 'X.Y.Z' released version of the extension to
+PostgreSQL. The corresponding Python extension will be installed in a
+virtual environment in `envs/X.Y.Z`.
+
+It can be activated with:
+
+```
+source envs/X.Y.Z/bin/activate
+```
+
+But note that this is needed only for using the package directly;
+the 'X.Y.Z' version of the extension will automatically use the
+python package from this virtual environment.
+
+The `sudo make deploy` operation can be also used for installing
+the new version after it has been released.
+
+To install a specific version 'X.Y.Z' different from the current one
+(which must be present in `releases/`) you can:
+
+```
+sudo make deploy RELEASE_VERSION=X.Y.Z
+```
+
+TODO: testing procedure for the new release.
+
+TODO: procedure for staging deployment.
+
+TODO: procedure for merging to master, tagging and deploying
+in production.
+
+## Relevant release & deployment tasks available in the Makefile
+
+```
+* `make help` show a short description of the available targets
+
+* `make release` will generate a new release (version number defined in
+  `src/pg/crankshaft.control`) into `release/`.
+  Intended for use by the release manager.
+
+* `sudo make deploy` will install the current release X.Y.Z from the
+  `release/` files into PostgreSQL and a Python virtual environment
+  `envs/X.Y.Z`.
+  Intended for use by the release manager and deployment jobs.
+
+* `sudo make deploy RELEASE_VERSION=X.Y.Z` will install specified version
+  previously generated in `release/`
+  into PostgreSQL and a Python virtual environment `envs/X.Y.Z`.
+  Intended for use by the release manager and deployment jobs.
+```