Tidy dependencies and style source code

• Initial GitHub release. For CRAN, fgeo.x and fgeo.tool must be released first.

Remove dependencies of measurements. This allows fgeo.tool to not depend on measurements.

Combine fgeo.abundance, fgeo.ctfs, and fgeo.habitat. This simpler structure has two main advantages:

• Allows installing fgeo without reaching GitHub's rate limit.
• Makes it easier to refactor functions within the same, expanded, package.