Add 'Environment::templates()' iterator

[SergioBenitez]

A mechanism to iterate over all loaded templates

[mitsuhiko]

I fixed the test on the branch so I merged it. I do wonder though if the name needs returning since template.name() returns it anyways.

[SergioBenitez]

I fixed the test on the branch so I merged it. I do wonder though if the name needs returning since template.name() returns it anyways.

The lifetimes for the strings are different, but I imagine it won't matter most of the time. I didn't realize there was a Template::name() -- I think it makes sense to just return an iterator over Templates in that case.

[mitsuhiko]

@SergioBenitez the lifetimes could in theory be adjusted by making Template::name() return the 'source lifetime which is probably a good idea anyways.