API v6.2 release (#43)

* set API_VERSION to 6.2

* add new transport block loop enabled/coef observables

* renoise.Application.current_song may be nil

* child views in rack, aligner and spacer can be defined via a new "views" property

* add renoise.DeviceParameter name_observable

* add new ModifierFlags to Dialog key_handler, deprecated ModifierStates

* add phrase line & column selection properties to renoise.Song

* add "code" font style

* add new button "style" property

* add new "describe_batch_undo" function to renoise.Song

* add new "mouse_handler" to rack and aligner view layouts

* add new "font", "align" and "secondary_color" properties to button

* add new "cursor" propery to View

* add new "swap_views" function to renoise.View
  deprecate "add/remove_child" in favor of "add/remove_view"

* add  new "origin" property for views and a new "stack" layout view

* add background style to aligner and deprecate style in rack, using  new background property instead

* add new ScrollBar widget to the viewbuilder

* add trigger_note_on/off functions to Song

* add new app.theme, to access theme colors from tools

* set Lua LS runtime version to LuaJIT without ffi

* add new canvas view

* add new metronome properties and new sample recording functions to Transport

* add new text "link" control to view_builder

* add disk_browser category and instrument/sample properties view access

* removed bit (will be auto imported with LuaJIT)

* add new sqlite bindings

* add new transport sync mode property

* add new renoise.Application:show_menu

* add new app.key_modifier_flags and dialog.focused properties

* add new color property to text view

* add new multiline_text selected_text property and new text orientation property

* add new color property to bitmap view

* add optional focus change notifier to custom dialog constructors

* add new tool.app_will_save_document_observable

* add optional `undo_redo_enabled` flag to SampleBuffer:prepare_sample_data_changes

* add new song.trigger_pattern_line function

* add new right_frame_is_visible property to ApplicationWindow

* add instrument box slot size

* add instrument tuning properties

* extend metronome_beats_per_bar range

* add new view.size property & deprecated with & height

* add new scrollbar.step property

* add new song.transport.sample_recording_sync_enabled property

* add new renoise.Song:is_undo_redoing

* add new phrase script properties

* add new "Script Editor" context menu identifiers for tools

* add new polarity properties to slider and rotary views

* add new `set_pattern` function to Sequencer

* add new Application.audio_plugin_effects/instruments_observable

* add table.unpack

* add new `editor_visible` property to InstrumentPhrase

* update License copyright year

* unify documentation of deprecated properties and functions

latest API 6.1 release