Issue #1865 - Clean up RPC help messages

Based on the proposal, update the help message of rpc methods
- strings arguments are in double quotes rather than square brackets
- numeric arguments have no quotes (and no default value)
- optional parameters are surrounded by round brackets
- json arguments are strings but don't use double quotes

Added 3 sections for the details
- Arguments: lists each argument, it's type, required or not, a default, and a description
- Result: The method result, with json format if applicable, type, and a description
- Examples: examples calls using bitcoin-cli and curl for json rpc call

Problems
- maybe this is too verbose
- lines might be too long
- description are not good or complete
- examples may be too much

src/bitcoinrpc.cpp

@@ -189,8 +189,13 @@ Value help(const Array& params, bool fHelp)
 {
     if (fHelp || params.size() > 1)
         throw runtime_error(
-            "help [command]\n"
-            "List commands, or get help for a command.");
+            "help ( \"command\" )\n"
+            "\nList all commands, or get help for a specified command.\n"
+            "\nArguments:\n"
+            "1. \"command\"     (string, optional) The command to get help on\n"
+            "\nResult:\n"
+            "\"text\"     (string) The help text\n"
+        );
 
     string strCommand;
     if (params.size() > 0)
@@ -206,7 +211,7 @@ Value stop(const Array& params, bool fHelp)
     if (fHelp || params.size() > 1)
         throw runtime_error(
             "stop\n"
-            "Stop Bitcoin server.");
+            "\nStop Bitcoin server.");
     // Shutdown will take long enough that the response should get back
     StartShutdown();
     return "Bitcoin server stopping";