Something wasn't (up)right

Fixed:

• Fix matching algorithm to avoid obviously "using up" the good matches on certain regions of the mosaic.
• Fix image rotation to turn source images upright before using them.

Tell Me How

Added:

• Add basic usage info to README

Fixed:

• Fix documentation comment on Mosaic constructor

Changed:

• Change maximum number of source images used from 1/2 down to 1/3 of the total number