✨ add newline command for formatting

Add `newline` command for formatting: in order to add a new line between multiple formulas
Transfoms `newline` (AsciiMath) on `\\` (TeX).

Ref. :
- https://www.overleaf.com/learn/latex/Line_breaks_and_blank_spaces
- https://en.wikipedia.org/wiki/Newline

Request from:
- plantuml/plantuml#1824

app/src/main/java/math/ASCIIMathTeXImg.java

@@ -432,6 +432,9 @@ public boolean hasFlag(Flag flagName) {
 			new Tuple("mathtt"  , "mstyle", "mathtt"  , null      , Ttype.UNARY                 ), //
 			new Tuple("fr"      , "mstyle", "fr"      , "mathfrak", Ttype.UNARY , Flag.NOTEXCOPY), //
 			new Tuple("mathfrak", "mstyle", "mathfrak", null      , Ttype.UNARY                 ), //
+
+			// newline for formatting: in order to add a new line between multiple formulas
+			new Tuple("newline", "mo", "newline", "\\\\", Ttype.CONST, Flag.VAL, Flag.NOTEXCOPY), //
 	} //
 	));
 

app/src/test/java/math/ASCIIMathTeXImgUnitTest.java

@@ -493,6 +493,10 @@ class ASCIIMathTeXImgUnitTest {
 		" f'''                                                     , {f}''' ",
 		" uArr                                                     , \\Uparrow ",
 		" dArr                                                     , \\Downarrow ",
+		" newline                                                  , \\\\ ",
+		" a newline b                                              , {a}\\\\{b} ",
+		" anewlineb                                                , {a}\\\\{b} ",
+		" a^2newlinea^3                                            , {a}^{{2}}\\\\{a}^{{3}} ",
 	})
 	void mathUnitTest(String input, String expected) {
 		final String res = cut.getTeX(input);

app/src/test/java/math/TestUnitTestGen.java

@@ -562,6 +562,13 @@ static void initAll() {
 // Arrow (PR 138)
 		"uArr",
 		"dArr",
+
+// Newline (see plantuml/plantuml#1824)
+		"newline",
+		"a newline b",
+		"anewlineb",
+		"a^2newlinea^3",
+
 	})
 	void test(String input) {
 		String res = cut.getTeX(input);