Adds outline flag to doxygengroup directive.

Although already been documented, the outline flag has not been
implemented to the doyygengroup directive. This commit adds
functionality for that. Additionally, it fixes
`create_group_render_filter` to hide the content of structs as well.
Fixes minor code issues.

- a forgotten variable definition
- duplicate flag entry
Tweak filter implementation and add outline docs

The implementation is just style.

The docs cover an example of outline working as expected.
Fix class & namespace docs to cover protected-members

And fix doxygengroup/namespace typo.
Add :outline: to namespace documentation with example

And fix up the warning message.
Merge class & struct implementations

As they should be basically the same thing. This introduces public,
private, protected & undoc control to structs.

We copy and paste the class documentation to the struct page and do a
find and replace.

We also add example struct sourced files.
Improve innerclass filter

So that innerclasses respond properly the :members: option having
specific members listed.

Otherwise we get all the public classes when specific members are being
listed as it just detects the 'members' option being there.

We also have to add a code path to pass the class name down to the
members filter as innerclasses are listed in the full namespaces and
outer classes. ie. testnamespace::StructClass::PublicClass, rather than
just PublicClass.
Merge branch 'addgroupoutline'
Add examples list to Readme
Add change log for recent history
Merge branch 'docs'
Breaking test: Unable to resolve multiple matches for function

When a function is both declared and implemented, doxygenfunction fails with the message:

Warning
doxygenfunction: Unable to resolve multiple matches for function “open_di” with arguments () in doxygen xml output for project “decl_impl” from directory: ../../examples/doxygen/decl_impl/xml/

View example in:
function.html#separated-declaration-implementation-example
Fix: Allows picking a named function without arg spe

Also if there are several candidates, if all candidates' arguments are
identical.
Move decl_impl example to specific folder

And extend the class example to have an impl file as well for
testing.
Update gitignore files to have clean repository

Tired of stuff lying around confusing the status but still want some of
that stuff for development.
Improve function argument handling for overloads

The previous approach tried to read appropriate data out of the xml
object hierarchy and use it to figure out which function overload to
use. Unfortunately it only looked at the first entry and so for 'const'
declarations it would only see the word 'const' rather than a useful
type.

Here we introduce a TextRenderer based on Sphinx's text rendering
functionality and use it to render the xml arguments to a text string
and then do the comparisons based on comparing that to the input string
of the directive. Should prove more accurate.
Add no-link options to clean up some warnings
Display potential matches when function arg matching fails
Fix documentation to reference correct args
Provide console & output lists of function mismatches

We change the warning mechanism so that we can provide the raw_text and
the nodes if desirable.

Then we use that functionality to provide a text list of the function
mismatch options for the console output and a literal block text list
for the actual output.