Peakrdl-regblock

**Updates:**
* Add option to override CPUIF address width. 25

**Updates:**
* Add UDPs that implement read & write double-buffering. 22
* Enables atomic access to wide registers, or groups of multiple registers
* See documentation for [Read Buffering](https://peakrdl-regblock.readthedocs.io/en/latest/udps/read_buffering.html) and [Write Buffering](https://peakrdl-regblock.readthedocs.io/en/latest/udps/write_buffering.html)
* Fix misinterpretation of `swacc` behavior. 21
* swacc is now asserted for *both* read and write accesses.
* Add new `rd_swacc` and `wr_swacc` UDPs to complement new `swacc` property behavior.
* See [details in documentation](https://peakrdl-regblock.readthedocs.io/en/latest/udps/extended_swacc.html)
* Add ability to generate a HWIF report file that shows flattened struct contents. 13
* Add support for extending user-defined CPUIF using the PeakRDL command line tool plugin discovery interface.
* See [details in documentation](https://peakrdl-regblock.readthedocs.io/en/latest/cpuif/customizing.html#entry-point-for-the-peakrdl-command-line-tool)

**Updates:**
* Add support for nonuniform regwidths and wide registers (where accesswidth < regwidth). 12
* Fix synthesizability of fields with msb0 ordering

**Updates:**
* Fix bug in hier mode hwif generation (17)
* Add support for CPU interfaces that have write strobes. 12
* Add APB4

**Updates:**
* Add identifier filter to prevent collisions with SystemVerilog keywords (14)
* Add PeakRDL command line application entry point hook

Switch to use regular non-namespaced package (See https://github.com/SystemRDL/PeakRDL/issues/4)