static bool dhcpSetup (const char *) implemented on dhcp.cpp

The static method dhcpSetup (const char *) is defined on EtherCard.h but is has not been implemented on dhcp.cpp

I need to configure the hostname of my Arduino application and I supposed that the already defined method was intended for this purpose.

Therefore:

1) I have created a constant called DHCP_HOSTNAME_MAX_LEN which holds the maximum size of the hostname. I chose a value of 32 for the constant, which seems enough for me.

2) I have used the constant in the definition of the hostname variable:
static char hostname[DHCP_HOSTNAME_MAX_LEN] = "Arduino-00";

3) I have modified the method send_dhcp_message() to adapt it to the variable-length hostname.

4) I have implemented the method dhcpSetup (const char *).
Add documentation on class BufferFiller
Merge pull request #130 from koocotte/master

Add documentation on class BufferFiller, this is a doc only change (only comments are affected)
resolved merge conflicts
fixed up patches
Merge branch 'luiscarlosgph-patch-1'
added optional argument to allow optional DHCP hostname to come from either flash (default) or RAM
Merge pull request #136 from WickedDevice/master

DHCP Hostname Support
Fixed a few spelling typos.
Merge pull request #138 from nuno-silva/master

Fixed a few spelling typos.
Fix to make library to work in local subnet.

Redmine issue: #540
Putting back original commit change

https://github.com/jcw/ethercard/commit/fb99d3f8c1a189e5d3ff824634bb7385d10c62e9
Merge remote-tracking branch 'origin/master'