Modify README and add comments for some cryptic methods

README.md

@@ -1,6 +1,6 @@
 # Biju
 
-[WIP] Biju is an easy way to mount a GSM modem to send, to receive and to delete messages through a ruby interface.
+Biju is an easy way to mount a GSM modem to send, to receive and to delete messages through a ruby interface.
 This is project is based on this [code snippet](http://dzone.com/snippets/send-and-receive-sms-text).
 
 ## Installation
@@ -20,19 +20,22 @@ Or install it yourself as:
 ## Usage
 
 ```
-@modem = Biju::Modem.new(:port => "/dev/tty.HUAWEIMobile-Modem")
+modem = Biju::Hayes.new('/dev/tty.HUAWEIMobile-Modem', pin: '0000')
 
 # method to list all messages
-@modem.messages.each do |sms|
+# it can take the status in argument
+# :unread, :read, :unsent, :sent, :all
+modem.messages.each do |sms|
   puts sms
 end
 
 # method to send sms
-sms = Biju::Sms.new(:phone_number => '+3312345678', :message => 'hello world')
+sms = Biju::Sms.new(phone_number: '+3312345678', message: 'hello world')
-@modem.send(sms)
+modem.send(sms)
 
-@modem.close
+modem.close
 ```
+
 ## TODO
 
 1. Write missing test for modem module.

lib/biju/hayes.rb

@@ -26,6 +26,10 @@ module Biju
       extended_error
     end
 
+    def close
+      modem.close
+    end
+
     def at_command(cmd = nil, *args, &block)
       command = ['AT', cmd].compact.join
       command_args = args.compact.to_hayes

lib/biju/pdu/encoding/gsm7bit.rb

@@ -35,14 +35,22 @@ module Biju
 
           string.scan(/../).map(&:hex).each_with_index do |octet, i|
             index = i % 7
+            # Only keep the bits for the current character and
+            # add relevant bits from the previous octet
+            # to get the full septet and decode the current character
             current = ((octet & (2 ** (7 - index) - 1)) << index) | next_char
 
             res = add_char(res, current)
             current_length += 1
 
+            # Break when the number of septet is reached
+            # to prevent to add a last @ when there is 7 septets.
+            # The last octet will have one more septet to ignore.
             break if length > 0 && current_length >= length
 
+            # Get the relevant bits for the next character
             next_char = octet >> (7 - index)
+            # When index is 6, next_char contains a full septet
             if index == 6
               res = add_char(res, next_char)
               current_length += 1
@@ -58,6 +66,9 @@ module Biju
           length = 0
 
           string.chars.each do |char|
+            # Look for the current character in basic character set and
+            # extension and concatenate the reversed septets to get
+            # full octets
             if get_septet(char)
               res << get_septet(char).reverse
               length += 1
@@ -67,9 +78,11 @@ module Biju
               length += 2
             end
           end
+          # Add necessary bits to get a full octet
           res << ('0' * (8 - (res.length % 8))) unless res.length % 8 == 0
 
           [
+            # Group by octet, reverse them and print them in hex
             res.scan(/.{8}/).map { |octet| '%02x' % octet.reverse.to_i(2) }.join,
             length: length,
           ]

lib/biju/pdu/phone_number.rb

@@ -21,6 +21,7 @@ module Biju
       end
 
       def length
+        # If the last character is 0xF, remove this one from length
         number.length - (number[-2, 2].hex >> 4 == 15 ? 1 : 0)
       end
     end

lib/biju/pdu/timestamp.rb

@@ -1,3 +1,5 @@
+require 'date'
+
 module Biju
   module PDU
     class Timestamp
@@ -8,13 +10,19 @@ module Biju
       end
 
       def timezone
+        # The last 2 digits of the timestamp are for the timezone
         timezone = timestamp[-2, 2].reverse.hex
 
+        # The MSB define the plus-minus sign. 0 for +, 1 for -
         sign = (timezone >> 7 == 0 ? '+' : '-')
+
+        # The following 3 bits represent tens digit
+        # and the last 4 bits are for the units digit
         tens_digit = ((timezone & 0b01110000) >> 4)
         units_digit = (timezone & 0b00001111)
 
-         sign << '%02d' % ((tens_digit * 10 + units_digit) / 4)
+        # Timezone is in quarters of an hour
+        sign << '%02d' % ((tens_digit * 10 + units_digit) / 4)
       end
 
       def to_datetime