Update SimpleToken.sol

Update ecrecovery.rst

Math.sol is not used, not needed

Add Slack notifications

Small thing, but the Math.sol is not really needed, since it is not used.

Use address(0) instead of 0x0

[TokenVesting] Add missing safemath ops

Fix typo

[TokenVesting] vestedAmount should return the historical vested amount

TokenVesting bugfix

Add token vesting

[TokenVesting] Fix vestedAmount calculation. Linearity test watches beneficiary balance over vestedAmount