add ansi_display, import in edd
now edd depends only on ansi_display, break dependence on vt_display, ansi, ascii
However ansi_display still depends on terminal
remove import terminal, define putstr in module
move pysh Python shell from piety directory to samples
rename from pysht to pysh
revise several README to explain modularity:
modules in samples must not import modules from pysh and vice versa,
modules in scripts import modules from piety and samples