Added calibration for each TEMPer device on the system.

TemperDevice.__init__() reads /etc/temper.conf if it exists, and calibrates each device which has a configuration line in the file.
Format of the config file is, for example,

Device 0: scale = 0.937, offset = -0.5625

(see CONF_RE in temper.py for details).
Calibration is made with the formula

y = scale * x + offset

where x is the raw value read from the device (in celcius), y is the calibrated value, and scale and offset are read from the config file.

Since TemperDevice class object doesn't know what device number it is assigned,
an argument "id" is added to TemperDevice.get_temperature() to tell it which calibration data line to use.
Added Joji Monma to README.md
Change the way TEMPer device identifies it's physical location.

TemperDevice now accepts "bus" argument in its __init__() method.
Initializer code looks upon usb sysfs directory using this bus and deviceID
information, and finds the port(or chain of ports) which this device is
plugged on. After that, it reads configuration file (/etc/temper.conf) and
uses calibration parameters found on the line with matching bus-ports.

This is needed to uniquely identify the physical location of a TEMPer device,
since only bus-ports combination can persist across reboots or connection
 losses.
Merge branch 'with-calibration' of http://github.com/GM3D/temper-python into with-calibration

Conflicts:
	temper/temper.py
Wrote README.md and temper.conf.sample

Adjusted regular expression for USB bus-ports pair, so that example
line can be commented out with a preceding hash mark.
Corrected typoes in README.md and temper.conf.sample
Bug fix in calibration related code

Instead of reading devpath from sysfs entry, use matched pattern for entry name itself.
Add error handling to readattr()
Fix regular expression to match sysfs entry
Untabified temper.py
Change \n to \r\n
Modified README.md

Merge "Usage" section of README.md to Instllation section since
temper/temper.py does not have it's own main() code.
Some documentation and spell checking.

Add some note about multiple devices in README.md
Minor spelling correction in temper/temper.conf.sample
Store ports as attribute in TemperDevice.

Store ports (string like "2.1.2") as an attribute so that it can be
used later for output. Modify find_ports() method accordingly.
Add bus-port info output to frontend.

Add -h option to temper/cli.py for usage help.
Add -p option to temper/cli.py for bus-port output.
Add get_bus() and delete get_location() in TemperDevice
Add description of -p option in README.md
Revert unnecessary named argument "id" in snmp.py
Merge pull request #2 from GM3D/with-calibration

Adding calibration code by GM3D, thanks!