cmake: Add CMake build system

    
- Reimplement the entirely of the autoconf, automake, libtool
  and pkg-config logic, including all feature tests
- Also include the MSVC logic missing from the above
- Include a full set of unit tests to reimplement the logic
  in sanityTest.pl and the data in sanityTest_ExpectedResult.logs
- Obtain versioning information from configure.ac and
  version.incl
- Generate and install exported CMake configuration for use by
  downstream projects using CMake, to replace FindXercesC.cmake
  provided by the CMake upstream
- Install documentation
- Add targets to regenerate the HTML manual and the Doxygen
  API reference portably, replacing the shell script and batch
  file for generating the manual
- Add targets for the documentation source files and
  substitute sources so that they are visible and editable in
  an IDE
- Library versioning continues to use the existing libtool
  naming and numbering conventions on Unix platforms:
  On Unix, the name has a -3.1 suffix before the library
  extension to match the libtool -release versioning behaviour.
  The symlink remains xerces-c for build time linking
- Library versioning continues to use the existing Visual
  Studio project file conventions on Windows:
  On Windows, the .lib and .dll names (and associated .exp, .ilk
  and .pdb files) use -3[D] and -3_1[D] suffixes
    
This will allow building with any supported build system on any
UNIX-like platform or upon Windows, as an alternative to the GNU
autotools and MSVC version-specific project and solution files
which will behave consistently across all platforms.
    
The only feature of autoconf and automake which is not converted
is "make dist", and that's absolutely possible should it be
desired.


git-svn-id: https://svn.apache.org/repos/asf/xerces/c/trunk@1797546 13f79535-47bb-0310-9956-ffa450edef68