Define new data structures and the corresponding function prototypes
New data structures and dynamic allocation

Code parameters have been regrouped into data structures, for a sake
of clarity. These data structures are dynamically allocated, so there
is no limit on the numbers of shells or reactions anymore. In addition
a new format of source model file has been implemented. This new
format allows to describe "time-dependant" sources, i.e. sources in
which the temperature, density, etc. changes as a function of
time. This new type of source has not implemented in solve() yet.
Update TODO file
Update AUTHORS file
Update NEWS file
Update .gitignore file
Update the URL for bugs on GitHub
Move the to-do list to GitHub
Update the README file
Update the bug report address in the documentation