Changes:

• phtrtest was rewritten to allow accessing a greater subset of Photoropter's functions;
• command line syntax is almost like in fulla now, with -r, -g, -b, -c and -x options;
• fulla-style PTLens TCA correction is complete now and produces results identical to fulla's;
• linear scaling model was implemented, which can be used both for image scaling and for simple linear TCA correction.