UEye_Camera: the color mode is now set as 8-bit monochromatic.
Image class: Added getter functions for the width and height.
Implemented the UEye_Camera acquire() method.

The function now sets the camera in trigger mode and generates a
one-shot image acquisition by software.
Image class: Defined the 'writeToPNG' function.

This function will write the image to the given PNG file.
Image class: included the libpng header.
Renamed the README file and described library dependencies.
Makefile: Added the libpng library to the list of libraries.
Image class: implemented the 'writeToPNG' method.

This method uses the libpng library to save the image to a PNG file in
persistent memory.
Image class: Added class documentation.
Added PPM files to the gitignore list.
Fixed bugs in the uEye camera single capture mode.
Makefile: the code is now compiled with debug informations.
Modified the main code to enable single capture mode.
Image class: added the 'writeToPPM' method.

This method writes the image to a '.ppm' file which can be easily
translated to various image formats using linux utilities.