fix: improve err messages for song imports

Signed-off-by: Martin Chodur <[email protected]>

feat: improve chords regexps

Signed-off-by: Martin Chodur <[email protected]>

feat: support import from songbook.fun

Signed-off-by: Martin Chodur <[email protected]>

fix: transpose also slash chords

Signed-off-by: Martin Chodur <[email protected]>

feat: add support for velky-zpevnik.cz and improve chords regexp

Signed-off-by: Martin Chodur <[email protected]>

feat: support lacuerda.net

Signed-off-by: Martin Chodur <[email protected]>

fix: kytarycz nbsp handling

Signed-off-by: Martin Chodur <[email protected]>

docs: document release process

Signed-off-by: Martin Chodur <[email protected]>