added cyg-boot option in makefile and small change to allow repositories with username/pwd

Hi, 

I added some small changes, which would be nice to have added to the code base:

- a new build target "cyg-boot" to use the build procedures under Windows with cygwin, so a Windows user could use the build instructions and also get the commandline (even though just cygwin) working as it is under Linux

- at least for the dev server I needed the artifact resolving to my.datomic.com, a repository with username/pwd and so far the :repository key just was a set
-> I changed it internally to use maps as pomegranate/aether does and distinguish just in the multi-method between the :repository value being a set or a map
-> the second part of the change is in boot.core

Michael