Add support for pipes in templates #53

The goal is to be able to modify values of variables used in templates.
It enables future functionality such as escaping, inlining etc.

It adds support applying predefined pipes to variables. Pipes
can be applied to variable substitution in with and parameter
substitution expressions. They work in similar way to piping in Unix
where each pipe applied to the compiled result of pipe before.

It adds support for using pipes in `with` and parameter substitution
expressions. It also refactors how their regex is build to reuse more of
the logic by abstracting regex building into a new class.

Finally, it separates and extends documentation for templating.

README.md

@@ -30,7 +30,8 @@
 - Have full visibility into what the tweaks do as you enable them
 - Ability to revert (undo) applied scripts
 - Everything is transparent: both application and its infrastructure are open-source and automated
-- Easily extendable
+- Easily extendable with [own powerful templating language](./docs/templating.md)
+- Each script is independently executable without cross-dependencies
 
 ## Extend scripts