Composer module

The Composer module consists of:

• the composer Python module for authoring compositions,
• the pycompose and pydeploy commands for managing compositions from the command line.

The documentation for the Composer package is organized as follows:

• COMPOSITIONS.md gives a brief introduction to compositions.
• COMBINATORS.md explains the composition constructs.
• COMMANDS.md describes the pycompose and pydeploy commands.