Expose built-in filters

[jannik4]

My current setup:

• I use tera in a webserver and use "slugify" to slug a name/text as part of an url
• In the route I want to check/compare the slugified part of the url with the slugified name

So it is important that I can use exactly the same slugify function in the rust code.

[Keats]

I guess if you don't mind having to convert it to a Value? I'll take a PR for it

[jannik4]

I think this would be ok.
Do you think just making the builtin module public would be good? This would obviously make builtin functions and tests public, too.
The alternative I can think of would be to reexport builtin::filters as builtin_filters.

[Keats]

Might as well just expose builtin

[Keats]

Ah the little issue with that plan is that every single function needs to be documented now if they are made public :(

[Keats]

That can be exposed after v1 release anyway, so not a blocker.