Help: Explain build/install-tree include dirs in more places (#14946)

Explain how to use $<BUILD_INTERFACE> and $<INSTALL_INTERFACE> directly
in the documentation of the target_include_directories command and
INTERFACE_INCLUDE_DIRECTORIES target property.  Otherwise readers need
to notice the link to the cmake-buildsystem(7) manual and find the
example in that to understand the need for these expressions.

Also fix the explanation in cmake-buildsystem(7) to not claim that
relative paths may be used inside a BUILD_INTERFACE expression.
Merge branch 'doc-include-dir-props' into release
Help: Use "^^^^" for subsubsection headers

This is the convention suggested in the Sphinx documentation and is
already used in several other places in the CMake documentation.
Update a few places where we were using other characters.
Help: Add documentation style section headers to cmake-developer.7

Give the style guides titles instead of numbers so we can link to them.
Help: Organize documentation style sections in cmake-developer.7

Now that the style guidelines have section titles instead of numbers,
organize them into more well-defined sections.
Help: Document section header underline hierarchy in cmake-developer.7

Explicitly specify the sequence of underline characters we use in the
CMake documentation.  It is the same sequence as that suggested in the
Sphinx documentation, but we have our own descriptions.
Merge topic 'doc-section-header-convention'

793b64e4 Help: Document section header underline hierarchy in cmake-developer.7
05bd31ab Help: Organize documentation style sections in cmake-developer.7
eaafe756 Help: Add documentation style section headers to cmake-developer.7
4207b3a3 Help: Use "^^^^" for subsubsection headers
FindQt4: Use standard section header underline convention

The FindQt4 module is a CMake Domain object of type "module".
Our convention for domain object document titles is "------"
and domain object document sections is "^^^^^^".  Switch to
these within the FindQt4 documentation.
Merge topic 'FindQt4-doc-section-underlines'

06ab7db3 FindQt4: Use standard section header underline convention
CMake Nightly Date Stamp
Merge topic 'doc-include-dir-props'

907e422b Help: Explain build/install-tree include dirs in more places (#14946)
Merge branch 'release'
Simplify and clarify credit text and link

Use the name "Kitware" rather than "Kitware, Inc." to simplify the text.
Provide a CMake-specific URL.
Merge branch 'cmake-credits' into release
Merge topic 'cmake-credits'

8da0a75b Simplify and clarify credit text and link
Merge branch 'release'
Simplify and clarify credit text and link

Use the name "Kitware" rather than "Kitware, Inc." to simplify the text.
Provide a CMake-specific URL.
Merge topic 'cmake-credits'

889f2fd8 Simplify and clarify credit text and link
Merge branch 'cmake-credits' into release
Merge branch 'release'