Quote filenames and title before using on command line

This commit quotes title and filename paramaters that are passed to the
command line when showing an image.
Closes #397. Fixed Viewer.show to return properly.

Viewer.show did not return a value, however ImageShow.show expected
Viewer.show to return a non-falsey value if successful. Therefor ImageShow.show
would continue to call multiple viewers.
Image.convert mode 1 documentation update. Fixes #407
Docs: Noted import change for Image Plugins. Fixes #404, plugin not found
fix compiling with FreeType 2.5.1
Merge pull request #427 from stromnov/master

fix compiling with FreeType 2.5.1
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Fixed memory leak saving images as webp when webpmux is available
Merge pull request #429 from cezarsa/master

Fixed memory leak saving images as webp when webpmux is available
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Merge pull request #408 from wiredfool/convert_doc

Image.convert mode 1 documentation update.
Merge pull request #409 from wiredfool/plugin_doc

Docs: Noted import change for Image Plugins. Fixes #404, plugin not foun...
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Merge pull request #399 from tmccombs/double

Closes #397. Fixed Viewer.show to return properly.
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Merge pull request #398 from tmccombs/escape

Quote filenames and title before using on command line
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