Reorganize the documentation into separate files

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

CONTRIBUTING.md

@@ -0,0 +1,90 @@
+# Development process
+
+Please read the Working Process/Quickstart Guide in README.md first.
+
+For any modification of crankshaft, such as adding new features,
+refactoring or bug-fixing, topic branch must be created out of the `develop`
+branch and be used for the development process.
+
+Modifications are done inside `src/pg/sql` and `src/py/crankshaft`.
+
+Take into account:
+
+*  Tests must be added for any new functionality
+   (inside `src/pg/test`, `src/py/crankshaft/test`) as well as to
+   detect any bugs that are being fixed.
+*  Add or modify the corresponding documentation files in the `doc` folder.
+   Since we expect to have highly technical functions here, an extense
+   background explanation would be of great help to users of this extension.
+*  Convention: snake case(i.e. `snake_case` and not `CamelCase`)
+   shall be used for all function names.
+   Prefix function names intended for public use with `cdb_`
+   and private functions (to be used only internally inside
+   the extension)  with `_cdb_`.
+
+Once the code is ready to be tested, update the local development installation
+with `sudo make install`.
+This will update the 'dev' version of the extension in `src/pg/` and
+make it available to PostgreSQL.
+It will also install the python package (crankshaft) in a virtual
+environment `env/dev`.
+
+The version number of the Python package, defined in
+`src/pg/crankshaft/setup.py` will be overridden when
+the package is released and always match the extension version number,
+but for development it shall be kept as '0.0.0'.
+
+Run the tests with `make test`.
+
+To use the python extension for custom tests, activate the virtual
+environment with:
+
+```
+source envs/dev/bin/activate
+```
+
+Update extension in a working database with:
+
+* `ALTER EXTENSION crankshaft VERSION TO 'current';`
+  `ALTER EXTENSION crankshaft VERSION TO 'dev';`
+
+Note: we keep the current development version install as 'dev' always;
+we update through the 'current' alias to allow changing the extension
+contents but not the version identifier. This will fail if the
+changes involve incompatible function changes such as a different
+return type; in that case the offending function (or the whole extension)
+should be dropped manually before the update.
+
+If the extension has not previously been installed in a database,
+it can be installed directly with:
+
+* `CREATE EXTENSION crankshaft WITH VERSION 'dev';`
+
+Note: the development extension uses the development python virtual
+environment automatically.
+
+Before proceeding to the release process peer code reviewing of the code is
+a must.
+
+Once the feature or bugfix is completed, all the tests are passing
+and the code has been accepted by peer reviewing,
+the topic branch can be merged back into the `develop` branch and a
+new Pull-Request can be created on it.
+CI-tests must be checked to be successful.
+
+The release manage will take hold of the PR at this moment to proceed
+to the release process for a new revision of the extension.
+
+## Relevant development tasks available in the Makefile
+
+```
+* `make help` show a short description of the available targets
+
+* `sudo make install` will generate the extension scripts for the development
+  version ('dev'/'current') and install the python package into the
+  development virtual environment `envs/dev`.
+  Intended for use by developers.
+
+* `make test` will run the tests for the installed development extension.
+  Intended for use by developers.
+```