Clarify and/or Improve Dev OMNI section in the specification

[msgilligan]

The Dev OMNI section in the Spec at the very least code use some clarification, but we may want to make some improvements as well.

Note that any changes should (at a minimum) not violate (at any blockheight/hash) either of the following rules:

1. Reduce the number of OMNI at the Exodus address enough so an existing valid SEND operation becomes invalid
2. Increase the number of Dev OMNI issued above the prescribed 10% of the Crowdsale

Current issues include:

1. Use of floating-point math in the specification (e.g. 1 - 0.5**y) -- accuracy and code portability issues.
2. Use of timestamps (which are not monotonically increasing) rather than blockheight
3. Use of Omni/BTC Mainnet values (magic numbers)
4. Possible differences from the reference implementation

Possible alternative implementation ideas include:

1. Specify an increase per-block that gets reduced (perhaps, halved) every `n' blocks (more similar to BTC block reward)
2. For BTC Main-net it may be necessary to have the spec changes activate at a specific block height.

Note that this specification change might be best approached through the OLE process.