radare2/libr/reg

** TO BE REMOVED ** THIS MODULE IS PLANED TO DISSAPEAR **

* Library to handle register values for multiple architectures
* Architecture register sets are handled as plugins?
* Designed to be used from radare libr within the modules:
  - r_vm : to properly setup the per-architecture register configuration
  - r_debug : to get/set register values
  - r_core : to display register values in 'd' (debug) command. dr

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We will have to split up every arch into a plugin
- define an API to access to registers and get info. about the type of regs.
- we can base this stuff as in r_vm is done

We must merge the r_vm reg stuff here too, its all about static, dynamic
and virtual analysis

-- add methods to transplant all registers from one side to other
 - allows to convert foo

TODO:
  - add support for sign/unsigned registers..or at least a way to cast them
  - add push/pop of register states (maybe we only need 2 levels of states)
    - can be used for diffing registers
    - is also useful to store values before emulating code
    - we can probably implement this in a clone() method? (too heavy? more orgtogonal)