modified parser to tolerate common faults

See merge request !8

* parse identifiers disregarding of case
* ignore license and readme files by filename
* special case for broken files only containing 0x00 bytes

Resolve "FileValidator Klasse"

Closes #4

See merge request !5

Resolve "Custom "DUET" Flag soll in den Parser eingefügt werden"

Closes #8

See merge request !7

* fixed spelling of duett to duet
* merged P1/P2 and DUETSINGERP1/2 to P1/P2

added walker for parsing

See merge request !6

Resolve "SongFile Parser"

Closes #2

See merge request !3

fixed: Ultrastarsongfile

See merge request !4

- zusätzliche tags die ultrastar unterstützt hinzugefügt
- andere tags werden als custom_tags gespeichert

will throw exception on invalid key

Data upload

See merge request !2

UltraStarSongFile Class

See merge request !1