Move formatting functions around.

The base64 and base32 functions used to be in crypto.c;
crypto_format.h had no header; some general-purpose functions were in
crypto_curve25519.c.

This patch makes a {crypto,util}_format.[ch], and puts more functions
there.  Small modules are beautiful!

src/common/include.am

@@ -68,6 +68,7 @@ LIBOR_A_SOURCES = \
   src/common/log.c					\
   src/common/memarea.c					\
   src/common/util.c					\
+  src/common/util_format.c				\
   src/common/util_process.c				\
   src/common/sandbox.c					\
   src/common/workqueue.c				\
@@ -122,6 +123,7 @@ COMMONHEADERS = \
   src/common/crypto.h				\
   src/common/crypto_curve25519.h		\
   src/common/crypto_ed25519.h			\
+  src/common/crypto_format.h			\
   src/common/crypto_pwbox.h			\
   src/common/crypto_s2k.h			\
   src/common/di_ops.h				\
@@ -135,6 +137,7 @@ COMMONHEADERS = \
   src/common/torlog.h				\
   src/common/tortls.h				\
   src/common/util.h				\
+  src/common/util_format.h			\
   src/common/util_process.h			\
   src/common/workqueue.h