Don't futz with $^W. Import warnings and remove import_warnings conf setting.

Use warnings->import when importing Dancer2 to ensure any code using it has
the warnings pragma enabled (just like strict and utf8).

L<perllexwarn> states ".. using $^W to either disable or enable blocks of
code is fundamentally flawed.". Also see Matt Trout's comments in #427.

Remove the import_config setting and its trigger that mucks with $^W and purge
it from the POD. If anyone really wants to set $^W, they can add it to their
app or psgi file and be in control of the results.
reflect change
Merge branch 'Pr/no_global_warnings'
call app in different way
consistency
reflect change
Merge branch 'pr/fix_374'
request/upload: all attributes --> 'ro'
(filename, tempname, headers, size)
request: some attributes --> 'ro'
(serializer, body_is_parsed, uploads, id, body, content_length, content_type, path, all of @http_env_keys)
document serializer as a getter
reflect change
Merge branch 'request-cleanup'
Test Template_Simple - from old Sukria branch
Update Changes
Merge branch 'pr/test_template_simple'