Remove Travis CI.

- Save some time

Serialized objects changed version from older versions of R.

Update doc read_network(): uniqueness of origin-destination data, invalidity of quotes in names, consistency of coordinates.

- Rather than the smallest which produced large rasters and bad performance in regions with a long form factor.

- Install some packages from binaries in Travis-CI

- Avoid installing source packages at all in Appveyor for preventing errors

- Install geonetwork from CRAN

- Caused errors installing in some locales (bug report Javad)

- This can occur for units to small to contain a raster cell centre, or that are small islands

- fixes #32

fixes #27