Enhancements to AppImage

Enhance 'build-appimage' script:

- add initial comment block and comments for all major steps in the
  script for the benefit of casual users of the script
- 'configure' to build HTML + PDF documentation
- do not remove the man pages from the AppDir (will be used by custom
  AppRun script)
- use a bigger icon
- use '-g' for appimagetool so it can figure out the 'updateinfo' string
  on Travis CI
- output big fat warning to users who build AppImage in non-"Trusty"
  environments

Add 'AppStream' metadata file

This serves to satisfy desktop environments who want to automatically
create menu entries, show screenshots and display software descriptions.

Note, this file (qpdf.appdata.xml) may need more tweaking since the
Freedesktop folks aren't exactly sure themselves how their 'standard'
should exactly look like, and they changed their validation tools
quite a bit over the recent years in incompatible ways...

Extended and enhanced customized AppRun script

- Add a '--ai-usage' invokation param to the AppImage which serves as
  a starting point to explore the other embedded options
- Support displaying of manual pages by running AppImage with added
  parameter '--man ...'
- Also include HTML/PDF documentation, READMEs and licenses into AppImage
- Support for more parameters: '--list-man', '--list-pdf', '--list-readme',
  '--list-license', '--list-html', '--list-exe', '--pdf', '--readme',
  '--license', '--html' and '--show-apprun'
- Support 'fix-pdf' and 'zlib-' as sub-commands (not just as symlinks)

1 files changed, 21 insertions, 0 deletions

diff --git a/README-appimage.md b/README-appimage.md
new file mode 100644
index 00000000..790d5d02
--- /dev/null
+++ b/README-appimage.md
@@ -0,0 +1,21 @@
+# Using the QPDF AppImage bundle (for Linux x86_64 systems only)
+
+First advice:
+
+- After downloading, you have to set the executable bit for any AppImage (for security reasons
+  this is disabled by default):   `chmod +x <name-of-application>.AppImage`
+
+- Run the QPDF AppImage with the '--usage' parameter to start learning some useful details about
+  built-in features of this specific AppImage.
+
+
+More tips:
+
+- You can rename the AppImage to any name allowed for file names on Linux. The '.AppImage' suffix
+  is not required for it to function. It will also work as expected if you invoke it from a
+  symlink. Using 'qpdf' as its filename or symlink name is OK. However, you may want to continue
+  using the QPDF package provided by your system's package manager side by side with the AppImage
+  bundle: in this case it is recommended to use 'qpdf.ai' as a short name for (or as the symlink
+  name to) the qpdf-<version>.AppImage.
+
+- [...more tips to come... work in progress...]