malloc.h is obsolete.
On OpenBSD MAP_ANONYMOUS is called MAP_ANON.
Fix undefined termcap symbols on OpenBSD.

E.g.:
/usr/lib/libreadline.so.4.0: undefined reference to `tgetnum'
/usr/lib/libreadline.so.4.0: undefined reference to `tgoto'
/usr/lib/libreadline.so.4.0: undefined reference to `tgetflag'
/usr/lib/libreadline.so.4.0: undefined reference to `tputs'
/usr/lib/libreadline.so.4.0: undefined reference to `tgetent'
/usr/lib/libreadline.so.4.0: undefined reference to `tgetstr'

Tested on linux too, works.
Mention that GNU make is required.

Does not build with BSD make.
Merge pull request #28 from vext01/openbsd

Make micropython build on OpenBSD.