[Fixes #105] Treat regular font as a one element collection when parsing

[Pietrek14]

When parsing a font that is not a collection, a check is performed that returns a FaceParsingError::FaceIndexOutOfBounds error if the index is not zero. It's a breaking change, but it's not hard to migrate to the new version.

[RazrFalcon]

Thanks. The test should be in tests/tables/main.rs. And there is no need to include the font file itself as well. The header part should be enough. Like this:

#[test]
fn font_index_overflow_on_regular_font() {
    use Unit::*;
    let data = convert(&[
        Raw(&[0x00, 0x01, 0x00, 0x00]), // magic
        UInt16(0),                      // numTables
        UInt16(0),                      // searchRange
        UInt16(0),                      // entrySelector
        UInt16(0),                      // rangeShift
    ]);

    assert_eq!(fonts_in_collection(&data), None);
    assert_eq!(
        Face::parse(&data, 1).unwrap_err(),
        FaceParsingError::FaceIndexOutOfBounds
    );
}

[RazrFalcon]

Thanks!