script: create sane error return codes for script validation and remove logging

Attempt to codify the possible error statuses associated with script
validation. script/types.h has been created with the expectation that it will
be part of the public lib interface. The other flag enums will be moved here in
a future commit.

Logging has also been removed in order to drop the dependency on core.h. It can
be re-added to bitcoind as-needed. This makes script verification finally free
of application state and boost!

src/Makefile.am

@@ -112,6 +112,7 @@ BITCOIN_CORE_H = \
   script/sigcache.h \
   script/sign.h \
   script/standard.h \
+  script/script_error.h \
   serialize.h \
   streams.h \
   sync.h \
@@ -235,6 +236,7 @@ libbitcoin_common_a_SOURCES = \
   script/script.cpp \
   script/sign.cpp \
   script/standard.cpp \
+  script/script_error.cpp \
   $(BITCOIN_CORE_H)
 
 # util: shared between all executables.