Changing the way of comparing version numbers + minor js change

[ghost]

1 / I corrected a javascript issue. I added a test before removing the two last characters of .plugin-version-author-uri html, because for me that was causing a wrong terminated link (cut a </a> into </). But I'm not very sure it still work as it is supposed to work, because I was unable to find a case the split should occur with my plugin, so I couldn't test it.

2/ Now uses version_compare php function instead of casting version number to float. This allows to use minor release version number with more than one dot (previously 1.2.3 was considered the same as 1.2 or 1.2.*)