ISSUE: there are clashing file names in the book/img directory

[evgenyfadeev]

For example 18-A.png and 18-a.png. On MacOS file names are not case sensitive, so it would be best that either files with one case variant renamed to something distinct, or removed.

Here is what I get after git clone on a mac:

modified:   book/img/18-A.png
modified:   book/img/18-B.png
modified:   book/img/18-C.png
modified:   book/img/18-D.png
modified:   book/img/18-E.png
modified:   book/img/18-F.png
modified:   book/img/18-G.png
modified:   book/img/18-H.png
modified:   book/img/18-I.png
modified:   book/img/18-J.png
modified:   book/img/18-K.png
modified:   book/img/18-L.png
modified:   book/img/18-M.png
modified:   book/img/18-N.png
modified:   book/img/18-O.png
modified:   book/img/18-P.png
modified:   book/img/18-Q.png
modified:   book/img/18-R.png
modified:   book/img/18-S.png
modified:   book/img/18-T.png
modified:   book/img/18-U.png
modified:   book/img/18-V.png
modified:   book/img/18-W.png
modified:   book/img/18-X.png
modified:   book/img/18-Y.png
modified:   book/img/18-Z.png
modified:   src/img/18-A.png
modified:   src/img/18-B.png
modified:   src/img/18-C.png
modified:   src/img/18-D.png
modified:   src/img/18-E.png
modified:   src/img/18-F.png
modified:   src/img/18-G.png
modified:   src/img/18-H.png
modified:   src/img/18-I.png
modified:   src/img/18-J.png
modified:   src/img/18-K.png
modified:   src/img/18-L.png
modified:   src/img/18-M.png
modified:   src/img/18-N.png
modified:   src/img/18-O.png
modified:   src/img/18-P.png
modified:   src/img/18-Q.png
modified:   src/img/18-R.png
modified:   src/img/18-S.png
modified:   src/img/18-T.png
modified:   src/img/18-U.png
modified:   src/img/18-V.png
modified:   src/img/18-W.png
modified:   src/img/18-X.png
modified:   src/img/18-Y.png
modified:   src/img/18-Z.png

[aerickt]

lol that's crazy.
fixed: 9237ad4

Thank you.