Add valid_pubkey?
Prefer Resolv::DNS to subshell and regexps

Benefits
  * support transparently both IPv6 and IPv4
  * avoid spawning a child process
  * friendlier to all Ruby VMs (especially jruby)
  * less brittle when avoiding regexps
Add support for decoding negative values in compact bytes (i.e. target bits).
Relocate Dogecoin reward calculation to independent class

This moves the Dogecoin block reward calculation into its own class, in the same style as used
for Namecoin. Additionally this corrects post-600k block rewards for Dogecoin.
Add next proof of work difficulty target calculation.
Corrected rounding of modulated time values for Dogecoin difficulty calculations
Support different hash types
Make the hash_type argument optional
Added BIP62 rule #6 support and test case derived from existing test transactions.
Implemented BIP62 rules 2, 3 and 4 based on Toshi code for malleability checks on transactions.
Added DER signature format validation and unit tests.
Added check to verify that the S-value on a DER signature is low.
Added test cases for compare_big_endian().
Enabled public key and signature BIP62 format checks when validating signatures.
Use https link for RDoc documentation
Add Tip4Commit badge
fix typo in README. close #144
minor cleanup in Script.compare_big_endian
P2SH scripts are now validated against BIP62 rules.
Added note about need to address signature generation once the BIP62 rules on
low S values have been finalised and Bitcoin Core implementation available as
a reference.