Shellerate

Added
- nop_sled(): creates a NOP sled
- XORity custom encoder
- math, asm_x86 and strings modules
- zero_with_and(): generates a shellcode zeroing a register using 2 ADD
instructions.
- get_esp_address_in_eax(): saves ESP value into EAX using push and pop
strategy

Changed
A lot of work it has been down on encoder classes. Biggest change is the
introduction of encoding strategies support. For such a reason, we must
implement specialized classes doing encoding.

The encoder.py file is moved on a adhoc directory and it will be the main
encoding class with all basic functionalities.

Added
- Adding Win32 bind shell shellcode (taken as is from msfvenom)
Changed
- Minor tweaks to binary script

Added
- Adding encoder class
- Adding encoder support for bind_shell shellcode

Added
- logging facilities in tcp bind shellcode
- added egg hunter generator for tcp bind shellcode

Changed
- now shellcode() is a method returning the internal shellcode representation.
From a semantic versioning point of view, this could reserve a major version
upgrade, however we didn't reach version 1.0.0 so I can bump only minor
version.

Added
- x86/Linux: TCP Bind shell shellcode added