Add a command to initialize a directory from a project template

[mfelsche]

We currently have some kind of template for setting up a new project: https://github.com/ponylang/library-project-starter but setting this up is a tiny bit cumbersome as one has to replace all variables defined therein somehow manually or with a custom sed script or the like.

My suggestion is somehow inspired by giter8 and sbt which exist in the scala world. With these tools it is possible to define a template as a github repository containing variable placeholders (and default values for some or all of these). And then just call sbt new <github-org>/<repo> to populate a directory with all the boilerplate for some kind of setup. There can be any kind of templates for different setups and different tastes. Creating them is actually super-easy.

It would be very awesome to have something similar for ponylang. This entails the following moving parts:

• a very simple templating engine (just replacing variables in files from a given set of values in a Map)
• a new stable subcommand (new would be my suggestion) that uses the template repository to template-replace all files into a given location
  • this should ask for values for every found variable in the template first before actually replacing them, or ask for input for them on hitting them in the process
• maybe this should honour a special file containing default values (e.g. .stable-new-defaults.ini)
• rework the https://github.com/ponylang/library-project-starter to be compatible with this setup

Any thoughts on this?

[SeanTAllen]

@mfelsche that is in line with what I was thinking re: ponylang/library-project-starter#1