bump version, tweak soft drop factor

Initial Hold- and Rotation System, refactor gravity level stuff (agai…

…n), remove line from endscreen information, refactor cmdline flag for custom layout, refactor add_modifier to be safe, change descent mode generation

Update README.md

add descent mode, bring back time trial, tweaks

include custom build tag in about menu

add hold, refactor code

remove spurious comment

appease formatter

tweak puzzle mode

update menu graph