Add lua expect(string)

Add simple expect functionality.

The expect(string) function will wait for input from the tty device and
only return when there is a string match. Regular expressions are
supported.

Example:

script = expect('password:'); send('my_password\n')

src/misc.c

@@ -20,6 +20,7 @@
  */
 
 #include "config.h"
+#include <regex.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -87,3 +88,27 @@ bool fs_dir_exists(const char *path)
 
     return true;
 }
+
+bool regex_match(const char *string, const char *pattern)
+{
+    regex_t regex;
+    int status;
+
+    if (regcomp(&regex, pattern, REG_EXTENDED | REG_NOSUB) != 0)
+    {
+        // No match
+        return false;
+    }
+
+    status = regexec(&regex, string, (size_t) 0, NULL, 0);
+    regfree(&regex);
+
+    if (status != 0)
+    {
+        // No match
+        return false;
+    }
+
+    // Match
+    return true;
+}