Fix compiler and ubsan warnings

[smnnlt]

While working on the R implementation of ezc3d I found some compiler and ubsan warnings generated by the C++ source code. I tried to remove them by making the following modification:

• Avoid integer overflow in hex2uint and hex2int by disregarding extra bytes. Also using bit shifting which should be faster and safer (0f99702)
• Catch by reference not by value in various functions (81b7345)
• Remove an unused variable in ezc3d::DataNS::AnalogsNS::Info::Info (61945bb)
• Fix correct comparison of signed and unsigned integers in ezc3d::c3d::frames (86f2bf6)

I have yet to get used to the test suite, so I have not tested the modifications so far (apart from the R implementation, where I could remove the warnings and the code still works as intended).

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This change is 

[pariterre]

Reviewed 11 of 11 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @smnnlt)

[pariterre]

Sweet again :) Thank for you help!