add .gitignore

.gitignore

+*.tar.gz
+*.exe
+*.dll
+*.do
+*.o
+*.lo
+*.la
+*.dylib
+*.dSYM
+*.mex*
+*.oct
+
+# generated code
+api/nlopt.f
+api/nlopt.hpp
+octave/nlopt_optimize_usage.h
+nlopt.pc
+swig/nlopt-enum-renames.i
+swig/nlopt-guile.cpp
+swig/nlopt-python.cpp
+swig/nlopt.py
+swig/nlopt.scm
+swig/nlopt.scm.in
+
+# executables
+test/testopt
+util/redblack_test
+
+# autotools stuff
+Makefile
+Makefile.in
+.deps
+.libs
+stamp-h1
+install-sh
+libtool
+ltmain.sh
+m4/libtool.m4
+m4/ltoptions.m4
+m4/ltsugar.m4
+m4/ltversion.m4
+m4/lt~obsolete.m4
+configure
+config.*
+autom4te.cache
+INSTALL
+aclocal.m4
+depcomp
+missing
+py-compile