Looks like we don't actually use them; when creating precompiled headers
with Visual C++, a dummy .cpp is created at build time.

ReST directive was used. Also fixed some other ReST directives that were
not correct and removed some warnings during buildbot checks.

- Used lunix style slashes - works on most systems
- Removed all trailing whitespaces

Invalid links and refences fixed.
SpaeseMat class documentation updated.

This reverts commit 4aaaef59.

Conflicts:
    modules/imgproc/include/opencv2/imgproc/types_c.h
    modules/legacy/include/opencv2/legacy/legacy.hpp