Consistent spellings of reentrant

Changed `rentrancy_lock` variable to `reentrancy_lock`

Burnable Token should be inherited from Basic Token issue#596

feat: RBAC authentication contract and role library

There's no need to throw when burning 0 tokens

Throwing when trying to burn 0 tokens is an unnecessary special case.
If another contract wants to burn() a variable amount, it should not be forced to deal with this special case of burning 0.

Minor standards and cleanup additions.

Add docs for DelayedClaimable

feat: remove yarn in favor of npm

fix: make SplitPayment payable by default

Address new compiler warnings

Minor formatting change