add to git
Add support for 64 bit VC compiler.
Use SHIFT+F5  to compile and run. Use SHIFT+F5 to compile PCH for x64.
test case: Switch 32 and 64 bit forth and back works
test case: interact 32-bit vim with 64 bit program works well. Checking with procexp, 64-bit application verified.
test case: gcc and pc-lint not be effected

lessons: when introduce new enumerator, in vim script, a new argument value 'msvc_x64', but not check all the branch
to make sure co-related variable be updated.
Merge branch 'master' of https://github.com/zhaorufei/CppSnippetCompiler