tabr 0.3.0 release

• Added fretboard_plot for making fretboard diagrams outside of the LilyPond tablature pipeline. This necessitates importing ggplot2.
• Added functions for phrase validation, coercion and decomposition back to original character string inputs.
• Added functions for note, pitch, chord and octave equivalence checks.
• Added a collection of functions for constructing and working with common chords. The chord constructors are among the chord_*-named functions and also have shorter x*-named aliases. These are "piano chords," i.e., based on the condensed, defining intervals.
• Added guitarChords dataset containing several thousand formations of guitar chord voicings.
• Added helper functions that use guitarChords for obtaining guitar chord information and mapping between different defining properties of a chord, most notably the addition of gc_notes and gc_fretboard for mapping chord names to noteworthy strings and fretboard diagram syntax.
• Added helper functions for working with basic note/pitch strings.
• Added helper functions for working with musical scales and modes.
• Added helper functions for working with musical intervals.
• Added noteworthy class, used internally, optional for users (includes custom print and summary methods).
• Added mainIntervals dataset.
• Added more internal checks of note and chord syntax validity across functions that work with string representations (pre-phrase object construction).
• Update older functions to utilize the new, more robust and stricter validation checks and offer more consistent noteworthy class output.
• updated transpose to handle additional edge cases, including a new style option, strip.
• Updated and added new unit tests.
• Bug fix for case where NA-valued no-chord rests (s or r) were unnamed in output of chord_set.
• Fixed entry in tabrSyntax.
• Fix class assignment bug and updated as_phrase.
• Added a new column of relative interval size to internal .keydata helper table.
• Added new vignettes focusing on the programming aspect of tabr.
• Updated documentation.