4.0.0 Roadmap

Please update this issue with more.

**Must-haves:**
- Delete the `html_*` plugins for good, because they're scary
- Delete the `count_*` plugins, because they're mostly unused
- Delete the `strip_tags` plugin, since it's most likely not safe
- Delete all plugins banned in strict mode
- Delete the following plugins, because they violate web best practices:
- `capitalize`: Use `text-transform` in CSS instead.
- `truncate`: Use `overflow` and `text-overflow` in CSS instead.
- `date_format`: Does not support proper localization, out of scope of Brainy.
- Remove the `make_timestamp` and `escape_special_chars` shared plugins, as they're only depended on by the plugins being removed above.
- Remove `$smarty->template`, which is banned in strict mode.
- Remove syntax features banned by strict mode.
- Remove support for built-in functions with side effects that are banned in strict mode: `reset()`, `current()`, etc.
- Remove `SmartyBC`.
- Remove the `inline` param from `{include}`.
- `{* set stricter *}` that requires all included templates to be strict

**Nice-to-haves:**
- AST-based parser and compiler
- Make it impossible to `{include}` or fetch a file outside of one of the recognized template directories.
- Mode that reports which assigned variables were not accessed
- API should be similar to `fetchedTemplate()` overridable method
- Should be enabled with a static flag
- May be possible to implement by making the scope array inside `TemplateData` be an object implementing PHP's `ArrayAccess` interface with zero overhead while mode is off (no new code branches)
- Make [`buildFilepath`](https://github.com/box/brainy/blob/master/src/Brainy/Resources/ResourceFile.php#L163) not be insane.

**Stretch:**
- 80% code coverage
- ~100% code coverage for bundled plugins
- Cut compilation times by 25%
- Reduce IO-related PHP calls (`filemtime`, `getcwd`, etc.) by 25%