Updating documentation for 3.1 release
Adding 3.2-prerelease version info
Test including an uncovered file.

Added file7.cpp, which is not covered by the test.
whitespace: Clean up trailing spaces and tabs
template: Move to jinja2
html: Make possible to output to a directory

Use the path separator to discriminate
-o name.html  -> filename name.html
-o dir/ -> filename dir/index.html
html: use Bootstrap
setup: Add jinja2
gcovr: Split data processing from the script
gcovr: Split xml reporting
gcovr: Split text output