Simplekml

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**Fixes**
* Changed pixel to pixels in class Units
* Removed a space in class RefreshMode

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**Fixes**
* Changed cgi module to html for Python 3

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**Fixes**
* Changed cgi module to html for Python 3

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**Changes**
* Removed email from source files
* Changed PyPi classifications for Python 3 to all versions of 3
* Updated readme by removing expired websites

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**Fixes**
* Made KmlElement class thread safe.
* Fixed formatting of gx:angles.

**Changes**
* Changed the license from GPL to LGPL

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**Fixes**
* Fixed "global" styles repeating in each container.
* Fixed ampersand (&) not escaping correctly in urls.
* Fixed problem where files added via :func:`simplekml.Kml.addfile` were forgotten.

**Changes**
* Moved the method :func:`simplekml.Kml.addfile` from being available from all classes to being available only via :class:`simplekml.Kml`