Fixed trailing comma in JSON structures and removed comments so
src/data/stations.json can be valid JSON.
Fixed stations data loading and parameters order in distance computation.
form-processing.js: select stations and return pollution data according
to parameters given by a form (passed as argument).
Very basic displaying of information returned by form processing.
Added src/php/pollution.php: php script returning pollution data
(as JSON).
Updated index.html with new javascript files. Now able to query
pollution information around some gps coordinates.