EEQ-BC charge model implementation.

What's Changed

• Exclude meson version 1.8.0 by @thfroitzheim in #54
• Fix for custom libs on Cray by @marvinfriede in #55
• EEQ-BC Implementation by @thfroitzheim in #56
• Bump mctc-lib to 0.5.0 by @marvinfriede in #58
• Bump version to 0.5.0 by @marvinfriede in #57

Full Changelog: v0.4.0...v0.5.0