Support for zero and negative exponents in plaintext power

Merge pull request #30 from aprismatic/negative_pt_pow

Add support for negative and zero plaintext powers

New constructor from an externally provided safe prime

If you already have a safe prime P that you like, you can now use it: var eg = new ElGamal(P);.
Constructor will check that it has bit length divisible by 8 and that it is indeed a safe prime.

Rename to ElGamal

0.13

Rename to ElGamal

Dependency Bump #2

Update to newest version of BigFraction

Dependency Bump

0.12.3.1

Dependency version bump

Deps bump for faster and correct operation

0.12.3

version bumps

Updated dependencies for faster key generation

Bump the BigIntegerExt to the latest version with slightly faster primality testing, which should make key generation faster.

Fixes to key generation

In v0.12, the key was not generated properly.

Breaking Changes

Breaking updates to the public API of the lib. The underlying homomorphism lib also has breaking changes.

BigIntegerExt Bump

Uses an updated BigIntegerExt that is guaranteed to generate a pseudorandom number of exactly given bit length, which slightly simplifies the key generation.