It makes a little bit more sense to have GeneratePublicKey as a method
of PrivateKey. In this case code doesn't need to check if caller
provided pointer is nil. Object was created by NewPrivateKey(), so it
code can assume object was correctly initialized.
The old GeneratePublicKey was returning an error when caller provided
pointer was nil. As this possibility is now removed, method doesn't
return error anymore.

* implements SIKE specified here:
    http://www.sike.org/files/SIDH-spec.pdf
  * methods for both - KEM and PKE - are added
  * adds SIKE specific key variant
  * tests: known answer tests for sike
  * uses cSHKAE from nobs-crypto

* tests: adds continues integration

* Makefile has targets for running tests, benchmarks and code coverage. It also
  contains target for env preparation. In order to run sidh tests
  GOPATH must contain p751toolbox package. I've chosen to manualy
  copy this package to the temporary GOPATH directory. It could also be done
  by calling "go get", but then any commit to both p751toolbox and sidh would need
  to be done in 2 steps.
* .travis.yml calls make and uploads code coverage to Codecov

* move sidh to seperated folder

* sidh: updates algorithm to SIDHv3 and refactoring

* makes an algorithm compatible with Microsoft's SIDHv3
  implementation. This is required to implement SIKE key
  encapsulation mechanism, as specified in PQC NIST submission
  from Nov, 30 2017
* removes SIDHBobPublicKey/SIDHAlicePublicKey/SIDHBobPrivateKey/
  SIDHAlicePrivateKey. Instead PrivateKey and PublicKey structures
  where introduced. Each of this structure stores variant of a key
  A or B. Implementation uses a key variant in order to differentiate
  between 2- and 3-torision groups.
  Main goal of removing "Alice" and "Bob" specific structures is to
  remove code duplication
* Introduces SidhParams: structure to store prime field and SIDH
  domain parameters.
* Refactors public API. Introduces:
    - Functions to generate, import, export keypair
    - DeriveSecret function to create shared secret
    - Supporting functions and types
* Removes code which is not used by implementation anymore, like
  DistortAndDifference(), SecretPoint(), DblAdd(),
  OkeyaSakuraiCoordinateRecovery() and many more. Also tests for those
  functions are removed.
* Adds fixes for key import/export