YW project file support

[tmcphillips]

Users need to be able to store settings for a YW-enabled project in a file. Here is a proposal for how it would work:

The project file will include any combination of the below:

• Default settings for command line parameters.
• A list of source files to process together.
• References to the source file and block that defines the top-level 'workflow'.
• Named styles for workflow graphs.

The project file will be yaml formatted.

If the project file name is named yw.yaml it will be read automatically when YW is run. Otherwise, the user will need to specify on the command line the prefix of the project file (with an expected .yaml extension) or the full path to a project file. Use of a project file will remain optional for basic operations. Some features, like graph styling, may require a project file.

There will be a YW command for writing a project file template to the current directory. This project file will include comments that document how to use it.

[tmcphillips]

Essential capabilities of the configuration files for YW are complete. Either a YAML file named yw.yaml or a Java-properties file named yw.properties (or both in combination) may be used.

Support for specifying the path to a configuration file explicitly or for writing out a default configuration file is no longer planned at this time.