Version 2.0.0

This release brings the following changes to the library:

• Breaking change: Minimum PHP version is raised to 7.0 since the library now depends on php-ds/polyfill.
• Travis CI tests are now run on PHP 7.0 and 7.1.
• New HmacHasher and Entity utility classes have been added.
• Enum gains getValues and getKeys methods.

New features:

• [8dce42c] Beakers: Import some useful classes from Nucleus (Eduardo Trujillo)
• [e6e3794] composer: Raise minimum PHP version to 7.0 (Eduardo Trujillo)

Updated documentation:

• [f430f5a] Hashing: Add description to HmacHasher (Eduardo Trujillo)

Chores:

• [bf4b252] travis: Run tests on 7.0 and 7.1 (Eduardo Trujillo)

Merge commits:

• [8041ea9] Merge pull request #9 from etcinit/nucleus-import (Eduardo Trujillo)