Changed a few words in Persian translation.

I fixed a few writing styles, and changed a few words with better translations. 

< code > tags in Persian are rtl, which is wrong, and must be ltr.

Also as a suggestion, Tahoma is not good for Persian when its representing non-small texts. Unfortunately there are not many options to choose a proper font for Persian language. I think, as many Persian websites are using DroidNaskh font and it is a stylish font, its better to change it to DroidNaskh which can be accessed from Google Web Fonts by:

@import url(http://fonts.googleapis.com/earlyaccess/droidarabicnaskh.css);
font-family: 'Droid Arabic Naskh', serif;