add comments to build_merkle_tree()
tidy up satoshiwords.cpp
performance improvement for deserializer.
improve examples with better comments.
comment code snippet for connect-simple example.
libsecp256k1 now has a pkg-config file so rely on that for autodetecting the pkg.
40% faster deserializer
add required libsecp256k1 to make flags
remove cruft
rename uninformative template parameter name CheckDistance to SafeCheckLast.

Also rename macro CHECK_DISTANCE to SAFE_CHECK_DISTANCE. Helps with
readability and makes pure intent of the code known just from looking at it.
allow unsafe deserialisation with transaction types.
replace serializer<Iter>::internal_copy() calls with std::copy()
add SafeCheckLast to satoshi_load for block_header_type
add index_type to blockchain
Merge branch 'origin/develop'
Fix unpretty iterator reference.