lensfun: Sample code

# Sample code

Here goes some coding examples, from simple to complex.

- example::c

This is a example written in pure C and it shows how to load the whole database, then prints it to stdout and finally saves the whole database to a new XML file.

- tfun::cpp

This is a more complex sample in C++ which shows how to do database lookups. The results found are saved to a new XML file.

- tmod::cpp

This is a more or less complex command-line application which can access most library functionality. It has been used as the main library testbed.