BugFix to `InTextNumberAppender`: `toString()` should work better now

The `toString()` method of `InTextNumberAppender` would more likely
return the raw number (like "2") instead of the textual representation
(like "two") for small numbers (for larger ones, this is the right
behavior). This has been fixed now.

Transition to Version 0.8.3

This commit marks the transition to version 0.8.3 of our software.

Minor Change to README.md

(just that)

Sqr, Sqrt, Cube, Cbrt now have 1-char ITextOut mathRender

We now can include arbitrary unicode characters into text strings of
arbitrary fonts (as we always use composite fonts and do not depend
on the limited character range of a given font anymore), as of the
previous commits. Therefore, we chose to represent Sqr, Sqrt, Cube,
and Cbrt by the corresponding unicode characters instead of function
names (no longer "sqrt(x)") and powers ("²" instead of "x^2").

Improved Maven POM and ConfigurationBuilder

Some errors have been fixed in the Maven POM: Minimization has been
turned off for the shaded full jar, as it leads to missing classes. The
main class now is specified correctly, too.

ConfigurationBuilder has been modified such that command line arguments
override config file arguments. I think this makes more sense than the
other way around.