docs: style and formatting cleanup

* Amends documentation to use more neutral, impersonal tone.

* Removes duplicated parts of the documentation.

* Fixes display of external images by using raw insertion.

* Adds CHANGES and LICENSE sections to documentation.

* Renames task example documentation sections.

* Simplifies README and uses it as long package description.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
setup: canonical repository and contact cleanup

* Uses `inveniosoftware` canonical repository URL and contact
  information in `setup.py`.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
global: MANIFEST cleanup

* Adds test files to MANIFEST as suggested by `check-manifest`.

* Removes `docs/make.bat` as we are not building documentation on
  MS Windows.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>