pimage: print error to stderr when detected an unaccepted pixel format
bugfix on linux: -strokedasharray should use relative to strokewidth
disable error: 'matrix ... is close to singular'
tkWinGDIPlusPath.cpp: remove trailing whitespace, tab-to-space

Rationale:
- Trailing whitespace caused tons of false differences at each commit
- Tab usage was VERY inconsistent in the source
ptext: added options: -fontslant {normal|italic|oblique}, -fontweight {normal|bold}
ptext: -textanchor: extended with n|w|s|e|nw|ne|sw|se|c
ptext: added -filloverstroke BOOLEAN option
pimage: added -anchor {n|w|s|e|nw|ne|sw|se|c}
pimage: implemented/added -fillopacity 0.0-1.0 -tintcolor COLOR -tintamount 0.0-1.0 options

WIN codes written by Andras Varga
pimage: added -interpolation {none|fast|best} option
pimage: added -srcregion { x1 y1 x2 y2 } option
implements arrowheads on pline, polyline, path objects
linux: pimage: bugfix: Cairo expects RGB premultiplied by alpha
doc: ptext: added -filloverstroke BOOLEAN option
doc: added pimage -anchor, -tintcolor, -tintamount, -interpolation
doc: pimage: added -srcregion
doc: implements arrowheads on pline, polyline, path objects
doc: pimage options moved to pimage
demos: ptext: added -filloverstroke BOOLEAN option
demos: pimage: implemented/added -fillopacity 0.0-1.0 -tintcolor COLOR -tintamount 0.0-1.0 options