Add EN_openX function

[LRossman]

EN_openX() allows an EPANET input file to be opened even if it has errors. This required re-arranging code, mainly in input3.c, so that default values are assigned to an object before its input line is parsed. Also a new function, validateproject(), placed in the new code module validate.c, is used to check for valid tank levels and pump curve coefficients that were formerly made in input2.c.

[lbutler]

@LRossman a very minor comment from me - I noticed that as part of this update you removed the undocumented ability to set the demand multiplier from within the [DEMAND] section.

The code that has been removed from input3.c is below:

EPANET/src/input3.c

Lines 801 to 807 in 7b64012

	// If MULTIPLY command, save multiplier
	if (match(parser->Tok[0], w_MULTIPLY))
	{
	if (y <= 0.0) return setError(parser, 1, 213);
	else hyd->Dmult = y;
	return 0;
	}

The only reason I know this exists is because we expectability ran into it affecting junction demands with ids start with the id mult*.

Interestingly this multiplier work with the GUI, but only with the keyword MULTIPLY, not MULT in the toolkit.

I was originally going to suggest maybe we depreciate it because it was causing issues with junctions but you've already done it here.

So my suggestion is that we include a note in the README that this undocumented feature was removed and that the multiplier be set inside the options.