Bugfix Maybe[Parameterized types] syntax in Core::Request

Parameterized types need square (not round) brackets.

With the types corrected, one less Request object is constructed during
the tests (due to a type failure).
Reflect changes
Merge branch 'bugfix/gh753_core_request'
Bugfix GH#753: seperate content get/set method.

The "before" modifier around the content accessor was called for both
gets and sets. The code was
  * modifying elements in @_, even when they were not variables, causing
    (fatal) warnings about "Modification of a read-only values".
  * when called as a getter, causing $_[1] to become vivified to an undef
    causing the actual accessor to consider it a set.

To solve this we add explicit reader/writer for the content attribute,
and a custom 'content' method to DWIM for get/set calls.

Also corrects the parameterized Maybe[] type syntax.

Resolves most of the "weird" test failures reported in #753.
(leaving the broken tests that involve the serializion of scalars)
Reflect changes
Merge branch 'bugfix/gh753_core_response'
correct Maybe usage
Wrap content setting in Response:

Instead of the solution in faaa685158e9432cc2ea3714e26a7df0e72824b7,
we use an "around" modifier to simply wrap the "content" method
to decide whether to serialize or not.

This removes the need for "set_content", "get_content", and having
both an attribute "content" and a method "content" (which itself is
either a setter or getter as well).
Fix deserialzier test:

The only change we're not sure about (but had to do) was to remove
the Encode::decode() call when returning parameters from the POST
request that had GET parameters with UTF8.

For some reason it was already decoded.
count :/
rewrite test, sort of, to fix the errors
more fixes
Merge branch 'fix/fix'