Limiting maximum elevation difference to protect from spikes

[ptrupek]

Due to some inaccurate elevation gain/loss data I found there's a plenty of GPX files from mobiles/watches with spikes in elevation (usually 100m> change).
This small adjustment checks if elevation delta is greater then allowed value in phpGPX::$ELEVATION_SMOOTHING_SPIKES_THRESHOLD to avoid spikes.

[Sibyx]

Hi @ptrupek, first of all, thank you very much for your contribution. Please check travis log (there was a code style issue), we use php-cs-fixer to fix that (configuration is already present in repository). Also, please add description for your feature in the README.md file (configuration section).

I you have any questions, feel free to ask.

[ptrupek]

I've formatted the code according to the code style, but there's nightly build in the travis, which is now PHP8 and is not compatible with phpunit/phpunit ^6.5

[Sibyx]

Yeah, I see (phpunit is already upgraded on develop branch), I don't want to mess around with php version on master (yet). 1.1.0 will be released (with your feature).