[FEATURE] Allow defining arguments for f:render with f:argument

[NamelessCoder]

This patch allows you to define arguments that get passed to
f:render by using f:argument in the tag contents.

<f:render partial="Something">
   <f:argument name="arg1">Special value for arg1 variable</f:argument>
   <f:argument name="arg2">Special value for arg2 variable</f:argument>
</f:render>

Any argument specified with f:argument this way will override
the argument of the same name if it was passed in the “arguments”
array as well. The combined result will be used as variables for the
sub-rendering call.

References: #427

[coveralls]

Coverage decreased (-1.0%) to 96.449% when pulling 0435601 on NamelessCoder:feature/slots into e3533d0 on TYPO3:master.

[NamelessCoder]

As a result of discussion:

• Feature changed so that f:argument is used to declare such arguments.
• Made the stack ViewHelper-class-agnostic so it will allow any VH to receive arguments this way as long as it fits the use case (works by evaluating tag content and then doing some output, not vice versa).
• Fixed various CGL and documenting comments.

[NamelessCoder]

Ready for another look @mbrodala (sorry about the ping, doing open-stuff-cleanups).

[mbrodala]

Looks good from reading (and amazingly simple) but I'd like to conduct at least a simple CLI test to get a feeling for this.

[NamelessCoder]

Just noticed that this comment is no longer correct, since removing the VH scope argument from the methods it relates to.

[NamelessCoder]

Abandoned; would not fit with Fluid 3.0 and is not vital.

[NamelessCoder]

Re-opened, there has been some interest for the feature and we should probably re-consider it. My plan is to either cross-port the API parts and functionality to the 3.0 branch, or create an identical feature there, to make 2.x and 3.x straight compatible concerning this particular feature.