Add .gitignore rules for in-tree builds.

This set of rules should cover make and ninja on Linux, and all of
nmake, ninja and vcxproj on Windows, so that if someone follows the
README build instructions (by doing 'cmake .' in-tree), it should
generate no debris that .gitignore can't filter out.

.gitignore

@@ -1,5 +1,21 @@
 *.o
-/Makefile*
+CMakeCache.txt
+CMakeFiles
+cmake_install.cmake
+Makefile*
+.ninja_deps
+.ninja_log
+build.ninja
+*.vcxproj
+*.vcxproj.filters
+*.dir/
+Debug/
+Win32/
+include/
+*.lib
+*.ilk
+*.pdb
+/*.sln
 /blackbox
 /bridges
 /cube
@@ -42,6 +58,7 @@
 /patternsolver
 /pearl
 /pearlbench
+/pearlsolver
 /pegs
 /range
 /rect
@@ -122,13 +139,18 @@
 /icons/*.ico
 /icons/*.rc
 /icons/*-icon.c
+/icons/*-icon-maker
 /icons/.deps
 /icons/.dirstamp
 /unfinished/divvy
 /unfinished/group
+/unfinished/groupsolver
 /unfinished/numgame
 /unfinished/path
 /unfinished/pearl
 /unfinished/separate
 /unfinished/slide
+/unfinished/slidesolver
 /unfinished/sokoban
+/unfinished/*.exe
+/*.desktop