* new scheme: chisel.axi is the main package
* chisel.axi.Axi4 contains the full axi defs
* chisel.axi.Axi4Lite contains the lite defs
* chisel.axi.axi4 contains full Axi4 impls
* chisel.axi.axi4lite contains lite impls
* same applies for the generators, matching structure

* moved DataWidth from top axi to Axi4/Axi4Lite objects
* cleaned generators, adopted new naming structure
* implemented generators for arbitrary register files
* master actions improved, simpler constructors
* master actions can be automatically generated from register file
* need to clean up the namespaces etc. - gotten really messy

* fixed some issues in ProgrammableMaster regarding wrong types of the
  response channels (was using old approach, direct UInt)
* fixed some issues in the register file spec, regarding peek/poke of
  non-IO fields, tests are functional

*  split into subpackages axi4 and axi4lite
*  moved each module into its subpackage
*  shortened names by removing Axi-prefixes wherever possible
*  moved Configs and IOs into corresponding companion object
*  replaced some printlns/printfs with Logging facilities

* AXI4Lite interface
* flexible ControlRegister class hierarchy: constants, single values,
  virtual registers (callbacks)
* implemented unit test cases
* had to implement Axi4LiteProgrammableMaster for batch testing