Fix Gentoo ebuilds

Fixed several issues:

* ebuild for libsodium was absolutely broken, I have no idea how this could have worked (pinging @Teknocrat for reference)
* fixed digests in Manifest files (@jedisct1: Please be careful when changing the ebuild files. Portage denies emerging packages if the digests in the Manifest file don't match the ebuilds)
* added dnscrypt-proxy-1.3.3.ebuild
* removed old ebuild versions since the packages are not existing in the downloads folder anymore

**Heads up to Gentoo users:** Emerging libsodium gave me a BIG error about conflicting files with the old dnscrypt-proxy ebuild. I'm not sure if it is possible to handle this in the ebuild, I just removed dnscrypt-proxy before updating.

Maybe relevant note: I use hardened-gentoo and noticed this warning when emerging libsodium:
```
 * QA Notice: The following files contain writable and executable sections
 *  Files with such sections will not work properly (or at all!) on some
 *  architectures/operating systems.  A bug should be filed at
 *  http://bugs.gentoo.org/ to make sure the issue is fixed.
 *  For more information, see http://hardened.gentoo.org/gnu-stack.xml
 *  Please include the following list of files in your report:
 *  Note: Bugs should be filed for the respective maintainers
 *  of the package in question and not hardened@g.o.
 * !WX --- --- usr/lib64/libsodium.a:stream_salsa20_amd64_xmm6.o
```
I don't know if this is an actual problem and if this needs to be fixed in libsodiums code or the ebuild, maybe someone has an idea.

PS: I hope this works now... Seems the new GitHub interface is confusing me ;)