Update help.txt: hex values, signed func fix

1) In the text file mode, it accepts a text file that contains hexadecimal values (instead of integers). I made this change because it would be confusing to ask users to convert their floating point values into fixed-point then into integers and then into unsigned integers. Now, they can provide hexadecimal values (refer to example.txt in the attached file).

2) In the function mode, it implements signed functions without changing the original equation. The tool prints out the input and output format as well.

Author: kiabuzz

help.txt

@@ -1,35 +1,41 @@
 Instructions
 -------------------------------------------------------------------
 This program generates source code  for  univariate  functions.  It 
-works in two modes: you can either (1) specify  a  .txt  file  that 
-contains the values of a look-up table specifying f(x)  for  all  x 
+works in two modes: you can either (1) specify  a  text  file  that 
+contains the values of a lookup table specifying  f(x)  for  all  x 
 values, or (2) describe the function by providing its equation.
 
-1) Lookup table as .txt  File  -->  Please  specify  the  following 
+1) Lookup table as a text File -->  Please  specify  the  following 
    arguments:
-	-table (string)		: the path of the table,  in  which 
-	                          each line has a  single   integer  
-	                          value.  The  table  size must  be 
-	                          a power of 2. 
+	-table (string)		: path of  the  table,   in   which 
+	                          each   line    has    a    single   
+	                          hexadecimal value. The table size 
+	                          must be a power of 2.  The  input
+	                          and   output   bit   width    are 
+	                          determined  based  on  the  table 
+	                          size  and  the  maximum  absolute    
+	                          value of the table, respectively.
 
-2) Function equation --> Please specify the following arguments:
-	-function (string)	: the  function's  equation  as   a 
+2) Lookup table as a math equation --> Please specify the following 
+   arguments:
+	-function (string)	: function's    equation    as    a 
 	                          string in quotation marks "".
 	-f_in (int)		: fractional  bit  width   of   the 
                                   function's   input.   Since   the 
                                   function is evaluated in  [0, 1),
                                   there are  no  integer  bits  for 
                                   the input.
 	-f_out (int)		: fractional  bit  width   of   the 
-	                          function's  output.  The   output 
-	                          integer bit width  is  determined 
+	                          function's output. The signedness 
+	                          and  integer  bit  width  of  the 
+	                          output       are       determined 
 	                          automatically.
 
 The following optional arguments can be used in either mode.
-	-name (string)		: output  table   and   file   name
-	-output (string)	: the   output   folder   for   the 
-	                          generated files. The folder  must
-	                          already exist.
+	-name (string)		: output table and file name.
+	-output (string)	: output folder for  the  generated
+	                          files. The  folder  must  already 
+	                          exist.                     
 	-mdbw (int)		: minimum decomposition bit  width. 
 	                          The default value is 2. 
 	-hbs (0/1)		: higher-bit  split.  The   default