Feature/add converters and bitwise ops (#20)

* added:

- converters
- bitwise operators
- hex input and output support

rpn.pod

@@ -109,6 +109,9 @@ Example of batch mode usage:
 If the first parameter to rpn is a math operator or function, batch
 mode is enabled automatically, see last example.
 
+You can enter integers, floating  point numbers (positive or negative)
+or hex numbers (prefixed with 0x).
+
 =head2 STACK MANIPULATION
 
 There are lots of stack manipulation commands provided. The most
@@ -136,6 +139,14 @@ Basic operators:
     x                    multiply (alias: *)
     ^                    power
 
+Bitwise operators:
+
+    and                  bitwise and
+    or                   bitwise or
+    xor                  bitwise xor
+    <                    left shift
+    >                    right shift
+
 Percent functions:
 
     %                    percent
@@ -157,19 +168,40 @@ Math functions:
     log10 log1p log2 logb pow round roundtoeven sin sinh tan tanh trunc y0
     y1 copysign dim hypot
 
-Commands:
+Conversion functions:
+
+    cm-to-inch
+    inch-to-cm
+    gallons-to-liters
+    liters-to-gallons
+    yards-to-meters
+    meters-to-yards
+    miles-to-kilometers
+    kilometers-to-miles
+
+Configuration Commands:
 
     [no]batch            toggle batch mode (nobatch turns it off)
     [no]debug            toggle debug output (nodebug turns it off)
     [no]showstack        show the last 5 items of the stack (noshowtack turns it off)
+
+Show commands:
     dump                 display the stack contents
+    hex                  show last stack item in hex form (converted to int)
+    history              display calculation history
+    vars                 show list of variables
+
+Stack manipulation commands:
     clear                clear the whole stack
     shift                remove the last element of the stack
     reverse              reverse the stack elements
     swap                 exchange the last two stack elements
     dup                  duplicate last stack item
-    history              display calculation history
+    undo                 undo last operation
+
+Other commands:
     help|?               show this message
+    manual               show manual
     quit|exit|c-d|c-c    exit program