Despite they look very similar (at least on Gnome on a Debian system),
the U+00B5 MICRO SIGN µ and the U+003BC GREEK SMALL LETTER MU μ are
different. We accept both as prefix.

Conflicts:
	src/main/java/org/orekit/utils/units/Lexer.java
	src/main/java/org/orekit/utils/units/Parser.java
	src/main/java/org/orekit/utils/units/Token.java
	src/test/java/org/orekit/utils/units/LexerTest.java
	src/test/java/org/orekit/utils/units/ParserTest.java