More OTCrypto work, plus preparing for Nym changes

Signed-off-by: FellowTraveler <F3llowTraveler@gmail.com>
Merge pull request #153 from happywarrior/master

changes to enable build for iOS
Abstracting OTMint/OTToken + OTCrypto. Also, I
renamed OTMasterKey to OTCachedKey.

Signed-off-by: FellowTraveler <F3llowTraveler@gmail.com>
Merge branch 'credentials'
Finished converting OTPseudonym to use OTKeypair.

Signed-off-by: FellowTraveler <F3llowTraveler@gmail.com>
Update docs for new linux tarball download location.
Merge branch 'credentials'
Merge pull request #154 from randy-waterhouse/master

Update linux docs for new tarball download location.