[MOD/FIX] Make the Parser API usable

It should now be good enough for parsing simple grammars(user IDs
for example)

src/Parser.c

@@ -26,6 +26,7 @@
 
 #include <Cytoplasm/Memory.h>
 #include <Cytoplasm/Str.h>
+#include <Cytoplasm/Log.h>
 
 #include <string.h>
 #include <sys/types.h>
@@ -72,7 +73,7 @@ ParserEndCopy(Parser * p)
 {
     char *ret;
     size_t len;
-    if (!p || p->mark >= 0)
+    if (!p || p->mark < 0)
     {
         return NULL;
     }
@@ -118,7 +119,44 @@ ParserExceptOneOf(Parser * p, const char * str)
         p->eof = 1;
         p->idx--; /* Avoid overflows */
     }
-    return !!strchr(str, strc);
+    if (strchr(str, strc))
+    {
+        return strc;
+    }
+    return 0;
+}
+
+int
+ParserGetc(Parser * p)
+{
+    int c;
+    if (!p || p->eof)
+    {
+        return EOF;
+    }
+    c = p->string[p->idx++];
+    if (!c)
+    {
+        p->eof = 1;
+        p->idx--; /* Avoid overflows */
+        c = EOF;
+    }
+    return c;
+}
+void
+ParserUndo(Parser * p)
+{
+    if (!p)
+    {
+        return;
+    }
+    
+    if (!p->idx)
+    {
+        return;
+    }
+    p->eof = 0;
+    p->idx--;
 }
 
 void
@@ -131,3 +169,4 @@ ParserEnd(Parser * p)
     Free(p->string);
     Free(p);
 }
+

src/include/Parser.h

@@ -53,9 +53,23 @@ extern Parser * ParserCreate(char *);
 extern int ParserExcept(Parser *, char);
 
 /**
- * Returns true if the character at the current position in 
+ * Gets the currently pointed at character in the parser, then 
- * the parsing process is one of the characters in the inputted 
+ * advances it by one, unless if hit by an EOF.
- * string, and advances by one character eitherway.
+ */
+extern int ParserGetc(Parser *);
+
+/**
+ * Rolls back the currently pointed character by one(unless already 
+ * at the start.)
+ */
+extern void ParserUndo(Parser *);
+
+/**
+ * Returns a non-zero value if the character at the current position 
+ * in the parsing process is one of the characters in the inputted 
+ * string, and advances by one character eitherway. 
+ *
+ * If non-zero, the return value is the actual character.
  */
 extern int ParserExceptOneOf(Parser *, const char *);
 
@@ -80,4 +94,5 @@ extern char * ParserEndCopy(Parser *);
  * .Fn ParserCreate .
  */
 extern void ParserEnd(Parser *);
+
 #endif                             /* TELODENDRIA_PARSER_H */