Update BUILDING.rst

Split sentences, improve build time estimate.
General source cleanup

Delete unused "experiments" directory, remove all trailing whitespace
from text files.
Use qmake builtin debug_and_release.
Remove OS-specific entries from .gitignore.

.gitignore should only store items that are generated by the code in the
repository. If your operating systems generates temporary files, put
those in your .gitignore_global.
README.md -> README.rst, update for new versions
Mv etc -> share, use applicationDirPath (fixes #30)

Also build outside of bin.
Log to stderr on Linux systems.

This fixes #114 and removes the write to the current directory that
places files where users may not expect.

I assume that Linux users are familiar enough with the command line to
run a program and output errors to a file via 2>file or similar.
Add .travis.yml, build out of bin