Make log_dir absolute path checking cross-platform
Add get_root_window method to App class

This comes in handy when the user needs the window instance without importing Window manually or using a Widget instance to call Widget.get_root_window.
When shortening plain label and even single word doesn't fit, shorten char by char from center.
When shortening markup label and even single word doesn't fit, shorten char by char from center.
When shortening, don't restrict width when laying out, otherwise single word might be split across lines, and when rejoined while shortening to single line a space would entered mid word when joining the lines.
Doc fix.
Don't change shorten_from when word is too long.
change method to property
Merge pull request #2169 from dessant/patch-2

Make log_dir absolute path checking cross-platform
Merge pull request #2171 from dessant/patch-3

Add get_root_window method to App class
Merge pull request #2175 from matham/shroten-short

Shorten fixes
Doc fix: label
Merge branch 'issue_2140'
Merge remote-tracking branch 'upstream/master'
Remnant of 1.4?
doc: added 'Getting started' for iOS dev
doc: added links for iOS tips + https support
doc: added missing example function, explanation on callbacks
Merge pull request #2185 from BoonsNaibot/patch-1

Remnant of 1.4?
doc: moved clang compiler issues to iOS compile docs