Identifiers starting with an underscore and followed immediately by a capital letter are reserved by the C++ standard.
The only header guards not fixed are those in the headers auto-generated from java.
There are now 2 encoding formats supported: 64-byte "compact" and DER.
The latter is strict: the data has to be exact DER, though the values
inside don't need to be valid.
The use of static makes this somewhat redundant currently, though if
we later have multiple compilation units it will be needed.
This also sets the dllexport needed for shared libraries on win32.
Dan Raviv
Gregory Maxwell
Pieter Wuille
Gustav Simonsson