Add support for the Pic language

samples/Pic/dextroamphetamine.chem

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+# Dextroamphetamine molecule
+.cstart
+	.ps 26
+	size 28
+R1:
+	ring double 1,2 3,4 5,6
+	bond 60 from R1.V2
+	bond 120
+A1:
+	front bond down ; CH3
+	bond 60 from A1 ; NH2
+	.ps
+.cend

samples/Pic/graph.pic

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+.PS
+	ellipse "Pic" "example"
+	arrow
+	box "This is" "a box" 
+	arrow right
+	box "Another" "box" dashed
+	move down then right;
+Thing: ellipse "This is a" "circle-thing"
+	arrow <-> from last box.r to Thing.l
+	move down then left;
+B: box "Still a box"
+	arrow from Thing.l to B.r
+	sprintf("Width = %g, Height = %g ", B.wid, B.ht) rjust at B.w
+	move down
+.ps 15
+	define sadness {
+		boxwid = 3;
+		boxht = 1;
+		textht = .5;
+		box "\"I run from my depression by" " " "burying myself in code\""
+		arrow down from last box.s
+		"Me"
+	}
+	sadness();
+.PE

samples/Pic/ritalin.chem

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+.\" RITALIN: Methylphenidate Hydrochloride
+.cstart
+.ps 15
+size 15
+	R1: ring double 1,2 3,4 5,6 pointing up
+	bond 60 length .35 from R1.V2 ; BP
+	bond 120 length .35 from BP
+	R2: ring pointing up put N at 1
+	H above R2
+	bond up  length .35 from BP ; BP
+	bond -60 length .35 from BP ; O
+	bond up
+	double bond 60 length .35 from BP ; O
+.ps 10
+.cend