Update for Visual Studio solutions

[Zuzu-Typ]

This pull request includes the following changes:

• removed old VS2005, VS2008 and VS2010 solutions (because they are no longer present in libogg anyway)
• added VS2015 solution
• added include path for "..\ ..\ ..\ogg", if you're using libogg as a GitHub clone
• merged vorbis_dynamic.sln and vorbis_static.sln to vorbis.sln (instead it uses Debug and Release for static and DebugDLL and ReleaseDLL for dynamic, which is how it's done in opus)
• using libogg.lib instead of libogg_static.lib when building dynamically, so someone who built libogg dynamically doesn't have to waste time and disk space building libogg statically.

Note#1: Merging this only makes sense if xiph/ogg#29 is merged too, because the new solution searches for libogg in e.g. DebugDLL

Note#2: The platform toolset of VS2015 is still v120, because I do not have Visual Studio 2015 on hand, so you might want to upgrade it to v140

I think this is everything I changed.

[tdaede]

Really old pr... but this needs to pass appveyor first.

[Zuzu-Typ]

Considering the nature of this PR, it's obvious it will never pass appveyor until the tests are adjusted.

Remember, the changes I made are supposed to make it easier to build ogg and vorbis by using the same approach as it's done in opus.

Please read the description at the top - it shouldn't be all that difficult to understand.

[tdaede]

Right, the appveyor.yml configuration is in the repo so you should be able to match it to the new solutions in this PR.