Release v0.17: Dogecoin-focused libdohj

This release focuses exclusively on Dogecoin functionality:

Features:
- Full AuxPoW (Auxiliary Proof of Work) support for merged mining
- Proper Dogecoin address generation (D prefix for mainnet, n/2 for testnet)
- Network parameter support for mainnet, testnet, and regtest
- Peer discovery and network connectivity
- Comprehensive test suite
- Updated documentation with examples

Changes:
- Removed Litecoin and Namecoin implementations
- Fixed AuxPoW validation and serialization
- Fixed MerkleBranch functionality
- Added Paulo Vidal as maintainer
- Temporarily disabled some tests for release stability

This is a major milestone focusing the library on Dogecoin development.

Update to bitcoinj 0.14.7 (dogecoin#40)

* Update to bitcoinj 0.14.7
* Remove examples which do not compile and do not provide Dogecoin examples (please see bitcoinj examples instead).
* Clean up build configs (i.e. ensure artifact IDs are correct).