Copying in miniz makes this difficult to use with projects that already use miniz

[johnboiles]

miniz is vendor'd into this repo, causing duplicate symbol linker errors if M5GFX is used in projects that already use miniz.

Not sure on the best way to handle this. Here are some options:

• Compile time flag that skips compiling miniz.c (assumes symbols will come from somewhere else)
• Rename symbols in miniz.c so they don't conflict with other projects using miniz

I'm running into this specifically in an esp-idf project where I have a miniz component already.

[lovyan03]

Hello, @johnboiles
I've updated the develop branch.
I've changed the names of symbols in the miniz, so I hope they won't conflict with miniz from other projects.
If there are no problems, this will be reflected in the next release.