Added document for pld component

docs/doc-pld.txt

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+
+devil1pld.h / devil1pld.c
+    Handles .pld files.
+
+File Format
+    PLDs are simple packages of different files, and do not contain a table
+    of contents. The header consists only of the number of files packaged
+    and the offsets from the beginning of the .pld that marks the starting
+    location of the file.    
+
+Functions
+    All functions are static but exposed by a function pointer in a constant
+    struct called DEVIL1PLD. For example, clients call functions using
+        DEVIL1PLD.getheader(..., ...);
+
+    bool getheader(struct PldHeader*, const char*);
+        Places file header into the struct pointed at by the first parameter
+        from the information given in by the second parameter.
+
+        inputs: pointer to a struct, pointer to file data
+                Neither parameter should be NULL.
+
+        output: true or false, whether or not operation succeeds or fails.
+                Will return false if one or both of the parameters are NULL
+                pointers.
+                Will return false if the attribute numOffset is less than 0-
+                i.e file is not valid.
+
+    int sizeofsector(struct PldHeader*, unsigned int i, unsigned int max);
+        Returns the size of the i-th file packed in the pld.
+
+        inputs: pointer to a struct, i-th element in pld, file size
+
+        output: (-1), [0, maximum value of int)
+                -1 indicates an invalid input.
+
+    void printheader(struct PldHeader*);
+        Shows contents of a PLD header in standard output.
+
+        inputs: pointer of a struct
+
+Example logic to iterate through a .pld
+    {
+        ...
+        // Get information about the file
+        struct PldHeader h;
+        DEVIL1PLD.getheader(&h, data);
+        
+        unsigned int i;
+        for (i = 0; i < h.numOffset; i++) {
+            const char *currentfile = filedata + h.offset[i];
+            ...
+        }
+        ...
+    
+    }