Collected API improvements

[jonpryor]

Collected API improvements while reviewing dotnet/android#89

Namespace should be Xamarin.Zip or Xamarin.Tools.Zip, not Xamarin.ZipSharp. A Sharp suffix adds nothing.

ZipArchive.NumberOfEntries should be named ZipArchive.EntryCount. Alternatively, maybe follow System.IO.Collections and have an Entries property of ICollection<ZipEntry> with a Count property.

ZipEntry.Name should be ZipEntry.FullName, a'la System.IO.Collections, if (I assume!) the value is the "full" name of an entry within the .zip file, e.g. foo/bar/baz.txt instead of just baz.txt.

ZipArchive.AddFile(string, CompressionMethod) should name the CompressionMethod parameter compressionMethod, not just method.

[grendello]

• changed the namespace to Xamarin.Tools.Zip
• renamed ZipArchive.NumberOfEntries to EntryCount. Using a collection of entries is wasteful (time and memory wise) as EntryCount simply calls a function in the native library that returns the number of entries read from the ZIP directory instead of iterating over all entries
• renamed ZipEntry.Name to ZipEntry.FullName
• renamed all the CompressionMethod method parameters to compressionMethod