gd.h now holds the canonical version number.

Up to now, the version numbers were defined in configure.ac and put
into gd.h by generating it from gd.h.in, replacing the values of
several C macros.  This violates the DRY principle, won't work on a
dumb build system, confuses some dev tools and is just a huge headache
in general.

This change makes gd.h (no longer generated) the home of the version
number and provides a script (config/getver.pl) which can extract the
requested version components from the header file.  configure.ac now
gets the version number from gd.h instead of vice versa.

In addition, there are now C functions that return the values of the
version macros.  This is for the benefit of non-C code using the
library without access to the header file.  It also provides a way to
get the version number of the library currently linked rather than the
header the program was compiled against.  (This could change if the
shared library is updated without recompiling the program using it.)
Test case for new version code.

This adds a simple test of the version API functions.
Updated Netware makefile

Makefile.netware (via an AWK script) used to pull the version numbers
from configure.ac.  Since they are no longer there, 'configure.ac' puts
them into 'configure' for Makefile.netware to find.  This change makes
it look there.

NOTE: This has not been tested on a Netware system.
Added new files to CMakeLists.txt.

Added new sources and tests to the relevant CMakeLists.txt files.

NOTE: This works for me but I am not a cmake expert.
Fixed a comment.

getver.pl comment referred to file src/version.h.  It should have
been src/gd.h.  This is now fixed.
Bug fix: tests didn't (always) return a valid status.

gdImageAALine_thickness.c didn't explicitly return 0 on success.

gdimageline_bug5.c was not an actual test at all.  It now confirms that the
tested operation (a line draw) alters the image it draws on.  (Not ideal
but better than what it did before.)
Added another Makefile.

This change adds a Makefile and bash script for building and testing
libgd on Windows with MinGW and MSYS.  This was written after I
concluded that it was easier and faster to just write a new Makefile
from scratch than to get autotools or CMake to play nicely with my
Windows installation.
Added beginnings of an updated manual

This changeset adds scripts and frontmatter for a user manual
for LibGD.  The manual is written using naturaldoc.  That is, the
actual manual (minus some front-matter taken from the manual for
version 2.0.36) is generated from specially-formatted comments in
the source code.

bootstrap.sh has been modified to also trigger generation of the
manual.
Added documention for gdImageCreate() and type gdImage.

This change adds naturaldoc comments for the above function and type.
Text was adapted from the 2.0.36 manual.

It also fixes the formatting of the comment for gdInterpolationMethod
so that naturaldoc will extract it.
Added .gitignore lines to exclude naturaldocs by-products.
Bug fix: gdImageScale() was sometimes messing up transparency.

_gdScaleOneAxis() was clamping the alpha channel to 0..255 when it
should be clamping it to 0..127.  This sometimes caused artifacts.

This change fixes that.