Have doc.go parse struct comments.

In code, structs that happened to have a '(' somewhere in their body
would cause the parser to go wrong. This change fixes that and updates
the comments on a number of structs.

Change-Id: Ia76ead266615a3d5875b64a0857a0177fec2bd00
Reviewed-on: https://boringssl-review.googlesource.com/6970
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/dsa.h b/include/openssl/dsa.h
index af439bd..1cf8489 100644
--- a/include/openssl/dsa.h
+++ b/include/openssl/dsa.h
@@ -128,7 +128,7 @@
 
 /* Signatures. */
 
-/* DSA_SIG contains a DSA signature as a pair of integers. */
+/* DSA_SIG_st (aka |DSA_SIG|) contains a DSA signature as a pair of integers. */
 typedef struct DSA_SIG_st {
   BIGNUM *r, *s;
 } DSA_SIG;