v0.0.8 - Maintenance Release

This is a maintenance release with dependency and CI updates together with some coder modernization changes.

Changes from PR #23:

• Upgraded CI from travis to GH Actions
• Node versions tested updated from [4, 5] to [10, 12, 13, 14]
• Upgraded dev deps (ethereumjs-block, nyc, standard)
• Added ethash_tests.json to test dir and removes ethereumjs-testing dep
• Use single imports for ethereumjs-util, upgrades to v7.0.2
• Modernizes buffer init syntax

Further/preceeding dependency updates in PR #19, PR #11, PR #8 and PR #7