REFACTORING: Template engine

[romaninsh]

https://github.com/atk4/atk4/tree/4.3-Template is dedicated to Template Parser refactoring.

The following are the requirements:

• Convert all templates into .YAML
• Change tags from <?..?> to industry-standard {}

Unfortunately due to some inline javascript our current template engine cannot properly interpret {} tags, so we need to implement them using preg_replace_callback.

Technically that's refactor of SMlite.

• [x] Rewrite parseTemplate which would recursively rely on replace_callback. It must be sufficiently smart to find matching template pairs.
• [x] Rewrite all templates using {} and YAML
• [ ] Test-cases
• [x] Benchmarks vs 4.2
• [ ] Benchmark vs RainTPL, Twig and Smarty

[romaninsh]

I have rewrote the algorithm here. Finally it works reliably, however I'm not sure about the performance. I'd like to back-port the new template engine and try it on 4.2.*

https://github.com/atk4/atk4/commit/e0b39a311b82c78d7d73b4c863e8e412472ca58d

[romaninsh]

Most of our templates are now using {} syntax and YAML.

[romaninsh]

This have been working pretty well.