Simplify options

[geraintwhite]

Remove node specific options and rename them to make them easier to understand.

[olls]

Suggested replacement options:

• build_cmd: string, a shell command to be run in repository root at processing stage
• copy_from: string, copy the contents of this directory to the output directory
• copy_to: string, the directory files should be copied to after processing
• output_cmd: string, a shell command to be run in output directory after processing
• ignore: list, a list of files and directories in the output directory that should not be overwritten/deleted
• url: string, a link to be displayed after processing on the github listener output
• email: list, a list of email addresses to send error messages if the build fails

[geraintwhite]

Wouldn't it make sense to keep some backward compatibility so we don't have to change all the configs?