Lambda-tools

This release adds some options to ensure that two consecutive builds of the same source code with no changes to the dependencies always produce exactly the same binary. This was not happening because timestamps in the files were not consistent.

* Adds an option `compile_dependencies` to the function configuration.

Release notes:

- Added an `ltools version` command.
- Made use of Docker optional and disabled by default. To enable it, add the option `use_docker = true` to your lambda definition.