Eliminate go_high, go_low syntax

[philipstarkey]

Original report (archived issue) by Ian B. Spielman (Bitbucket: Ian Spielman, GitHub: ispielma).

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For no apparent reason digital lines behave different from analog lines. For example I propose instead:

do_line.go_high(t)
becomes:
do_line.constant(t, 1) or
do_line.constant(t, True)

this allows uniform syntax across analog and digital lines, and makes programming do lines with variables more natural. Realistically the go_high/low methods would remain, but be depreciated.