Issue description

I currently use the library to serialize and deserialize GPX for analysis.
Some files contain elevation values greater than 1000m.
For these files the elevation is serialized with a comma as "thousand separator".
When the serialized GPX data is deserialized, Double.parseDouble is used,
which does not support the given Syntax.

Steps to reproduce the issue

1. Generate a GPX object with at least one waypoint which has an elevation greater 1000m
2. Serialze the object with the GPX.Writer#write method
3. Deserialize the object with the GPX.Reader#read method

What's the expected result?

• No exception is thrown
• The deserialized object contains exactly the same data

What's the actual result?

• A java.io.InvalidObjectException Exception is thrown

Additional details

Code

GPX gpx = GPX.builder()
        .addWayPoint { wp ->
            wp.ele(1234.5).build(1.2, 3.4)
        }
        .build()
String gpxString = GPX.Writer.DEFAULT.toString(gpx)
GPX result = GPX.Reader.DEFAULT.fromString(gpxString)

Stacktrace

java.io.InvalidObjectException: Invalid GPX: Invalid value for 'ele': For input string: "1,234.5"
	at io.jenetics.jpx.GPX$Reader.read(GPX.java:1183)
	at io.jenetics.jpx.GPX$Reader.read(GPX.java:1209)
	at io.jenetics.jpx.GPX$Reader.fromString(GPX.java:1271)