core: Add allocating b64 checksum functions

The checksum_b64_inplace variants can't be used in bindings. Provide
versions that allocate and return the output rather than working on a
passed in buffer. These can then be used in GI bindings to get the
ostree modified base64 encodings.

Closes: #398
Approved by: cgwalters

src/libostree/ostree-core.h

@@ -192,6 +192,8 @@ guchar *ostree_checksum_to_bytes (const char *checksum);
 _OSTREE_PUBLIC
 GVariant *ostree_checksum_to_bytes_v (const char *checksum);
 _OSTREE_PUBLIC
+guchar *ostree_checksum_b64_to_bytes (const char *checksum);
+_OSTREE_PUBLIC
 void ostree_checksum_b64_inplace_to_bytes (const char *checksum,
                                            guint8     *buf);
 
@@ -199,6 +201,8 @@ _OSTREE_PUBLIC
 char * ostree_checksum_from_bytes (const guchar *csum);
 _OSTREE_PUBLIC
 char * ostree_checksum_from_bytes_v (GVariant *csum_v);
+_OSTREE_PUBLIC
+char * ostree_checksum_b64_from_bytes (const guchar *csum);
 
 _OSTREE_PUBLIC
 void ostree_checksum_inplace_from_bytes (const guchar *csum,