Handling of non-standard framerates provided as strings (and additonal exports for ease-of-use)

[wfoxall]

Non-standard framerates provided as strings

When constructing a Framerate with a string, any value that does not match a 'standard' framerate (e.g. "25", "29.97DF"...) is now tested to see if it can be interpretted as a number.

If it can, it is parsed as a float and the framerate constructed from that number.

Framerate getter

Since a Framerate or FramerateLike object must be specified when constructing a Timecode, it makes sense to allow that Framerate to be retrieved from the Timecode instance later via a new getter.

Additional exports

• TimecodeError is exported so that consumers can test if an error is instanceof TimecodeError.
• A new const array of strings called StandardFramerates which contains the supported standard framerates is exported. Internally, the type definition of type StandardFramerate is defined as any of the values in that array.