Sceptre

- Increasing maximum number of boto call retires from 5 to 30.
- Adding support Jinja rendering for stack templates.
- Adding stricter requirements for existing stack state when launch
environments.
- Adding `cmd` hook for better cross platform support.
- Adding documentation around architecture of Sceptre projects.
- Adding versioned documentation.
- Improving documentation formatting.
- Fixing path error bug when using environment level commands on Windows.
- Fixing bug to correctly throw an AtrributeError in a Python stack template.

- Fixing bug for `protect` in stack config.

- Respect --dir when loading custom resolvers and hooks.

- Include Scope in `update-stack-cs` output.
- Updates to documentation.

- Removing deprecation notices.
- Updating documentation.

- Changing syntax used for resolvers and hooks in config files.
- Deprecating use of `sceptre_get_template` function in Troposphere templates.
- Deprecating the accessing of Troposphere templates returned from
`sceptre_get_template`.
- Deprecating the accessing of Troposphere templates from the global variable
`t`.
- Deprecating the global variable `SCEPTRE_USER_DATA`.
- Adding support for `sceptre_handler` function in Troposphere templates.
- Adding support for pure CloudFormation JSON strings returned by
`sceptre_handler`.
- Adding support for `sceptre_user_data` passed to `sceptre_handler`.
- Fixing bug in update-stack-cs.
- Adding project-variables resolver.