command args: trim leading/trailing whitespace

When certain commands in tasksh (such as 'review N') contain whitespace,
such as:

    review '1     '

The whitespace would tokenise into the command arg vector, effectively
treating the whitespace as a literal component.

In the case of the 'review' command, this is undesirable.  Therefore,
strip out all leading/trailing whitespace from the command args vector.

Fixes GH issue GothenburgBitFactory#43

src/main.cpp

@@ -39,6 +39,8 @@
 #include <readline/history.h>
 #endif
 
+#define WHITESPACE_CHARS " \t\n\r\f\v"
+
 // TODO These conflict with tw commands. This needs to be resolved.
 //      Perhaps an escape, such as '-- help' could invoke local help, or using
 //      a 'task' prefix could disambiguate.
@@ -113,7 +115,13 @@ static int commandLoop (bool autoClear)
   }
   else if (command != "")
   {
-    auto args = split (command, ' ');
+    std::vector<std::string> args;
+    std::string n;
+    for (const auto& s : split (command, ' '))
+    {
+       if ((n = trim(s)) != "")
+	 args.push_back(n);
+    }
 
     // Dispatch command.
          if (args[0] == "<EOF>")                      status = -1;