Introduced two new methods:

powerOff():
This will put the enc28j60 module into the sleep mode.

powerOn():
This will wake up the enc28j60 module back from sleep mode.

Usage:

void loop()
{
  Ethernet.maintain();
  [...]
  Ethernet.getNetwork().powerOff();
}
Fixed compiler warning in _eatBlock.
Fixed compiler warning by rearranging class variables in declaration.
Fixed compiler warning.
Fixed compiler warning.
Fixed compiler warning.
Fixed compiler warning about comparison between signed/unsigned.
Merge pull request #46 from nilrog/upstream

Fixed compiler warning in _eatBlock.
remove unused uip-neighbor as it's for ipv6 only
Merge branch 'upstream_miscfix' of https://github.com/nilrog/arduino_uip into nilrog-upstream_miscfix

Conflicts:
	utility/uip-neighbor.c
Merge pull request #49 from nilrog/upstream_36

Fixed compiler warning in UIPEthernet by rearranging class variables in declaration.
fixed compiler warning: 'upper_layer_memlen' may be used uninitialized in this function
Merge branch 'upstream_35' of https://github.com/nilrog/arduino_uip
save 12 bytes by avoiding unnessesary conversions from signed to unsigned int
saved aprox. 120 bytes of flash by declaring UIPEthernet internals static
save 150 bytes of flash by replacing 16-bit pointers by 8-bit array-indices in UIPClient
allow only 2 inbound UDP-packets instead of configurable array saves another 150 bytes of flash
save another 26 bytes of flash by using uint8_t instead of uint16_t for 8-bit enc28j60 register
adjust define for NUM_MEMBLOCKS to match previous commit
auto-free block when udp-packet is read entirely