crypto: move crypto business into a separate library

Crypto in Tarantool core was implemented and used very poorly
uintil now. It was just a one tiny file with one-line wrappers
around OpenSSL API. Despite being small and simple, it provided a
powerful interface to the Lua land used by Lua 'crypto' public
and documented module.

Now the time comes when OpenSSL crypto features are wanted on
lower level and with richer API, in core library SWIM written
in C. This patch moves crypto wrappers into a separate library
in src/lib, and drops some methods from the header file because
they are never used from C, and are needed for exporting only.

Needed for #3234