Change: Refactored nethandler

Separated functions in the nethandler package to their own files based on purpose.
Add: Experimental read and write support

Dev note: The program is prone to suspicous behaviour, i.e. crashing and freezing. Be aware.
Fix: Added missing file from last commit
Fix: No limbo-state after chrash and read functionality WIP

Program no longer gets stuck in limbo state after replacing calls to syscall.Read() with os.File.Read().
Write functionality in progress, currently crashes the program.
Fix: only write data back to nbd when responding to a read request, fixes #28

Add: debug print of packet
Also add checking of magic field in packets from nbd.
Add: debug print function of packets
Fix: making sure to read all bytes from connection

When reading from a connection, the Read(b []byte) function doesn't always read up to len(b). To fix this, a new helper function is impemented.
Fix: lots of fixes, Add: uses a map for mapping nbd handler with ivbs sequence

New helper functions to make sure bytes are read and written to connections and files.
Change: using net.TCPConn instead of net.Conn
Merge pull request #29 from demonicblue/blue-go

Add: Working read and write functionality (sort of)