capture ruby block in erb and slim templates, fixes #1582

[ujifgc]

ref #1582

This patch allows this weird stuff:

ERB:

<%= content_tag(:a) { content_tag :b, 'c' } %>

Slim:

= content_tag(:a) { content_tag :b, 'c' }

It was not working before because __in_erb_template and __in_slim_template flag was set in the preamble for generated ruby code and these flags were affecting behavior of #content_tag called with ruby or template block.

@minad, @padrino/core-members better suggestions would be appreciated

[minad]

Uh, that looks really bad. I have to think about it.

[minad]

It also doesn't work in haml for me.

[minad]

I found a much nicer solution: Please take a look at #1586. It is fixed for erubis, but it would also require a patched Slim version (2.0.2), which I haven't released yet. But I will do that if you want to accept the patch in this form.

[minad]

Slim patch is here: slim-template/slim@c5ed58d

The question is if it would be ok for you to require Slim >= 2.0.2 if I would release that.

[ujifgc]

I added failing tests to master and rebased this PR.

@padrino/core-members should we force Slim >= 2.0.2 or maybe skip the test for earlier versions?

Erubis extension can be fixed individually with no dependency impact.

[minad]

UPDATE: I reopened a new pull request which works with current Slim as is.

#1588