Merge pull request #105 from SlashDevin/master

Implement general-purpose microsecond timer
Rectoring of RTC::Timer (first increment).
Back to absolute time in RTC::Timer. Some further cleanup.
Merge branch 'master' of https://github.com/SlashDevin/Cosa into SlashDevin-master

Conflicts:
	cores/cosa/Cosa/RTC.cpp
	cores/cosa/Cosa/RTC.hh
Fixing problem with CosaBenchmarkRTC after latest change to RTC::Timer.
Refactoring RTC::Timer measurement sketch.
Minor formatting.
Minor format change.
Adding a new benchmark with sizeof information.
Update of benchmark documentation with latest run data.
Fixed formatting error.
Fixing formatting error.
Trying a new format.
New code block format.
Reversing order in News section.
Adding support for binary (4-bit) to hex character ('0'..'f').
Add support for MAC address print out in hex/colon format.
Improving W5100 Ethernet controller driver.

1. Introducing dev_flush() to remove contents of receiver buffer.
2. Fixing disconnect() so that the socket receiver buffer is flushed. Hardware
does not do this automatically.
3. Introducing get_addr() to allow access to network address and subnet mask
when using DHCP style begin.
4. Cleanup bind() and reduction of code in begin().
Removing RTC user level interrupt handler. Replaced by RTC::Timer.
Several improvement.

1. MAC address print out in hex/colon format.
2. Reuse INET print out functions.
3. Read line from request and print with uptime/request number.