Throw an exception for US-ASCII when getting bytes for codepoint > 0x7f.

US-ASCII is a 7-bit encoding so when writing bytes for codepoints > 0x7f,
an exception should be thrown.  This is required so that Integer.chr
correctly raises a RangeException for invalid values.
Whitespace fixes from @tychobrailleur.
Cleanup pom.
Tests for...

Throw an exception for US-ASCII when getting bytes for codepoint > 0x7f.

US-ASCII is a 7-bit encoding so when writing bytes for codepoints > 0x7f,
an exception should be thrown.  This is required so that Integer.chr
correctly raises a RangeException for invalid values.
Move all tests to a package consistent with jcodings' own.