move linux CI from configure to qmake. (#613)

move linux CI from configure to qmake. (#613)

- Add recipe for internal_styles.cc, xcsv_tokens.gperf, gui, unix-gui, toolinfo to GPSBabel.pro.
- Add support for text substitution in setup.iss and gbversion.h to GPSBabel.pro.
- fix qmake warnings from "qmake -Wall".
- split recipes for documents into scripts.
- shellcheck fixes for fixdoc, mkcapabilities.
- parallel build for coverage.
- add INSTALL file with build instructions.
- sort document targets into ones for general consumption (gpsbabel.html, gpsbabel.pdf) and one to support www.gpsbabel.org (now gpsbabel.org instead of index.html).