Specify coinbase constraints. fixes #81

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

protocol/protocol.tex

@@ -5099,8 +5099,8 @@ The encoding of $\joinSplitPubKey$ and the data to be signed are specified in
   \sproutonlyitem{The \transactionVersionNumber{} \MUST be greater than or equal to $1$.}
   \saplingonlyitem{The \transactionVersionNumber{} \MUST be \todo{}.}
   \item If $\versionField = 1$ or $\nJoinSplit = 0$, then \txInCount{} \MUSTNOT be $0$.
-  \item A \transaction with one or more coinbase inputs \MUST have no \transparent outputs
-        (i.e.\ \txOutCount{} \MUST be $0$).
+  \item A \transaction with one or more inputs from \coinbaseTransactions{} \MUST have no
+        \transparent outputs (i.e.\ \txOutCount{} \MUST be $0$).
   \item If $\nJoinSplit > 0$, then \joinSplitSig{} \MUST represent a valid signature
         over $\dataToBeSigned$ as defined in \crossref{nonmalleability}.
   \item If $\nJoinSplit > 0$, then \joinSplitPubKey{} \MUST represent a point of order $\ell$
@@ -5109,7 +5109,11 @@ The encoding of $\joinSplitPubKey$ and the data to be signed are specified in
         less than $2^{255}-19$.
   \sproutonlyitem{The encoded size of the \transaction{} \MUST be less than or equal to
         $100000$ bytes.}
-  \item \todo{Coinbase maturity rule.}
+  \item A \coinbaseTransaction{} \MUSTNOT have any
+        \joinSplitDescriptions\sapling{, \spendDescriptions, or \outputDescriptions}.
+  \item A \transaction{} \MUSTNOT spend an output of a \coinbaseTransaction
+        (necessarily a \transparent output) from a \block less than 100 \blocks prior
+        to the spend.
   \item \todo{Other rules inherited from \Bitcoin.}
 \end{consensusrules}
 
@@ -6350,6 +6354,9 @@ Daira Hopwood, Sean Bowe, and Jack Grigg.
 \subparagraph{2018.0-beta-9}
 
 \begin{itemize}
+    \item Specify the coinbase maturity rule, and the rule that \coinbaseTransactions
+          cannot contain \joinSplitDescriptions\sapling{, \spendDescriptions, or
+          \outputDescriptions}.
 \nuzero{
     \item Delay lifting the 100000-byte \transaction size limit from \NUZero to
           \Sapling.