FitFile remove caching of messages

[xmedeko]

Fix #59

[xmedeko]

@dtcooper @pR0Ps Do you agree to break backward compatibility a bit with this PR?

[pR0Ps]

I'm ok with breaking backwards compatibility, but only in the cases where the version is bumped to reflect it (ie semvar).

In this case, I don't think it's worth it by itself. It's not doing anything new or different, it's just removing a feature. If there are other breaking changes happening then this can go in with them, but IMO it's not worth breaking backwards compatibility just for this.

[xmedeko]

@prop This saves a lot of memory. So is necessary when running fitparse on a server.

I think more BC changes should be made to fitparse in regards of speed. So, a version bump is necessary. Better to discuss it somewhere else.

[dtcooper]

What about an argument when instantiating FitFile's __init__ method to turn on/off the message cache?

[xmedeko]

@dtcooper Yes, an extra parameter would do the job, too. But IMO the FitFile has too many responsibilities and should be broken to more classes. See #72 for my proposal.

[pR0Ps]

Implemented in 08d49be