Simplify the version bump process. ### Description

Simplify the version bump process.

- Use substitution hook in docs to update CDN URL.
  - In `dev` or `prerelease` versions, it will point to `dev` url
  - In `stable` versions, it will point it `vX.Y.Z` url
- Introduce a version bump script `tools/bump_version.py`.


~- Use `bump2version` to bump Python versions (continuing from #2460)~
~- Use `npm version` to bump JS versions~
~- Update `run_docker` script to use latest deployed pre-built docker image when `--pre-built` option is specified.~

### Checklists

- [x] Add new / update outdated documentation

package:
  name: cytoolz
  version: 0.11.2
source:
  sha256: ea23663153806edddce7e4153d1d407d62357c05120a4e8485bddf1bd5ab22b4
  url: https://files.pythonhosted.org/packages/b7/a9/9437d8e6a8ba420cb52832a4895614c61bf574bfb3978d5b0806b8ab95be/cytoolz-0.11.2.tar.gz
requirements:
  run:
    - nose
    - toolz
test:
  imports:
    - cytoolz

package:
  name: cytoolz
  version: 0.11.2
source:
  sha256: ea23663153806edddce7e4153d1d407d62357c05120a4e8485bddf1bd5ab22b4
  url: https://files.pythonhosted.org/packages/b7/a9/9437d8e6a8ba420cb52832a4895614c61bf574bfb3978d5b0806b8ab95be/cytoolz-0.11.2.tar.gz
requirements:
  run:
    - nose
    - toolz
test:
  imports:
    - cytoolz
