Resolve "Remove Sassc"

Closes #91

See merge request decker/decker!43

Resolve "Use native Haskell copy"

Closes #81

See merge request decker/decker!41

Recognise development builds of decker more precisely

Closes #107

See merge request decker/decker!47

Resolve "Reload delay for "decker server" is too high"

Closes #98 and #39

See merge request decker/decker!46

Resolve "Font handling is broken"

Closes #100

See merge request decker/decker!42

- Subdirectories in a project can be excluded from globbing and
  watching using the `exclude-directories` meta data property.
- Globbing times on the decker repo are down from 5 seconds to
  6 milliseconds.
- Some major restructuring and refactoring was necesssary.

Implemented cp and copyDir, including checking for differences and only copying files missing in destDir. `decker support` is relatively slow now, though (5-8s)