Pimp my .bashrc

To be honest I didn't even use my previous .bashrc, I just sticked
with the default .bashrc file Ubuntu generates after a fresh
install. However, it's time to change.

I've created my own .bashrc file. It's organized into sections.
Each section runs a batch of commands and defines a set of functions.
Most important sections right now are:

* Sensor related functions. They provide functions to read sensor
  values. Eg: temperature level inside the computer, battery status...
  Each sensor has a function for reading the value and a function to
  test if the computer has that device.

* Git related funtions. For instance, which branch I'm in or
  if this repository is dirty or not.

* My current PS1 configuration. I spent a lot of time working on
  this. I made my PS1 prompt line longer yet more useful and more
  beautiful by adding some information that I consider relevant
  and making it look nice with some colors. My PS1 displays:
  - battery level, if the device has a battery (e.g. laptop)
  - fan temperature.
  - user, host and folder, as usual.
  - if it's on a git repository, information about the repository.