Add a basic signing tool.

This is mostly to make it easier for me to generate test Ed25519
certificates.

Change-Id: I45e42f556d949d62eb6cdf684194958fa9f909bf
Reviewed-on: https://boringssl-review.googlesource.com/14504
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/tool/internal.h b/tool/internal.h
index fd66e00..80c9dc9 100644
--- a/tool/internal.h
+++ b/tool/internal.h
@@ -65,6 +65,8 @@
                  unsigned default_value,
                  const std::map<std::string, std::string> &args);
 
+bool ReadAll(std::vector<uint8_t> *out, FILE *in);
+
 bool Ciphers(const std::vector<std::string> &args);
 bool Client(const std::vector<std::string> &args);
 bool DoPKCS12(const std::vector<std::string> &args);
@@ -78,6 +80,7 @@
 bool SHA384Sum(const std::vector<std::string> &args);
 bool SHA512Sum(const std::vector<std::string> &args);
 bool Server(const std::vector<std::string> &args);
+bool Sign(const std::vector<std::string> &args);
 bool Speed(const std::vector<std::string> &args);
 
 // These values are DER encoded, RSA private keys.