Fixes #235.

Auto-indent mode leaves trailing spaces on blank lines as you type past them, so silently elide them from the window content as it gets written back to disk. Another option would be to remove them from the window entirely during Put, but they're actually nice to have while editing, and to date Put has never modified the window content.

FreeBSD 11.2 by default does not have gcc.

Use the widely accepted /dev/stdout.

My MacBook Pro has hw.ncpu=12, so set NPROC=12. Speeds up INSTALL dramatically. Should probably add similar code to other OSes. Also silence rio warning from earlier commit.

If $font is not set, the default font is constructed from font data linked into every libdraw binary. That process was different from the usual openfont code, and so it was not hidpi-aware, resulting in very tiny fonts out of the box on hidpi systems, until users set $font. Fix this by using openfont to construct the default font, by recognizing the name *default* when looking for font and subfont file contents. Then all the hidpi scaling applies automatically. As a side effect, the concept of a 'default subfont' is gone, as are display->defaultsubfont, getdefont, and memgetdefont.

Paint first appeared in 9front. The 9front license is reproduced in the related source files - the original repository is located at https://code.9front.org/hg/plan9front.

Fixes #98.

The only difference from the upscaled 16x16 is a one-pixel adjustment in the offset position, but this at least exercises setcursor2.

Using plain 'clang' does not work well for the new devdraw on macOS 10.14. But 'xcrun --sdk macosx clang' does work, for reasons no one understands. Hopefully this will be OK on all macOS systems.