termcap is not needed on Linux.  Need to work out how to automatically
configure the Makefile...

Make micropython build on OpenBSD.

Does not build with BSD make.

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.

Support Readline history and make it optional

Readline is GPL, so linking with it casts the binary GPL.

Updated to reflect build requirements for Ubuntu/Mint linuxes

Minor fixes

Trivial fixes for building unix version