Add smart_strings.py
Added command line switches, fixed UTF-16, UTF-32 reading
- Added command line switch '-t' to be compatible with traditional strings
- Added --readable-percent switch that takes over the function of '--readable' to specify a percentage of expected readable characters
- Removed '-m', '--max' switch to specify maximum string length
- Changed '--readable' switch to not take an argument and require 80% of readable characters
- Changed error handling of input decoder to 'ignore' so that invalid unicode sequences will not result in an error

Signed-off-by: Jonas Zaddach <zaddach@eurecom.fr>