encode content before using as in memory file

File handles should always have content in encoded form, not as unicode
characters.  perl 5.17.9 starts warning about this for in-memory file
handles.  This encodes the content used in the test before using it in
an in-memory file handle.
Allow the default template file extension to be changed.

apoca on IRC pointed out that it seems impossible to do this; the old
default_tmpl_ext config setting has no effect.

This looks to be the best fix (and will work for all template engines).
Er, config setting should be 'extension'.
Tests for changing template extension
Add on_plugin_import function to Dancer2::Plugin

This allows plugins to register code blocks to be run
on every import() and get the importing app's DSL object.
fix name of Dancer2::Manual::Hooks
fix github links
link SEE ALSO entries in tutorial
Dancer -> Dancer2 in a few pod links
Merge pull request #204 from haarg/fix-request_upload

encode content before using as in memory file
Merge pull request #189 from haarg/doc-fixes

Fix a few pod issues
Merge pull request #208 from dagolden/topic/on-plugin-import

Add on_plugin_import function to Dancer2::Plugin
Merge pull request #206 from PerlDancer/dave/change_tmpl_ext

Support changing template file extensions
Improve Dancer2::Plugin documentation

Specifically, give better examples of using the DSL object.

Also fixes various Dancer1/2 typos from a prior global search and
replace.