Various bug fixes for experimental version

git-svn-id: https://svn.code.sf.net/p/vcftools/code@897 19d466ce-640d-45be-954f-fad4d9839663
Added functions to filter INFO tags based on values. Updated the documentation

git-svn-id: https://svn.code.sf.net/p/vcftools/code@898 19d466ce-640d-45be-954f-fad4d9839663
Merge remote-tracking branch 'upstream'