Add new tests to backends and architecture;
Merge commit "Add regression test for Yosys PR 896"

backends
=======
1. backends/firrtl/firrtl.cc – skipped because of error:
 ERROR: Unclocked write port 0 on memory top.ram.
Add model with memory block too, so you can cover line block starting at
line 419

simple
=========
+ 1. passes/techmap/attrmap.cc
There is example in help block create example with
(* keep="true" *) attribute and run example

+ 2. passes/techmap/dff2dffe.cc
execute with  -unmap parameter

+ 3. passes/techmap/dff2dffs.cc

+ 4. passes/techmap/extract.cc
Lot of variations of input parameters is not excersised

? 5. passes/techmap/extract_counter.cc
This is specific to greenpak4 architecture, but idea is to have counter
in design and call this after synth_greenpak

+ 6. passes/techmap/shregmap.cc.
This also seams to be greenpak4 specific, but extracting shift register

misc
========
1. passes/techmap/insbuf.cc

Testing problems:
1. backends/firrtl/firrtl.cc – skipped because of error:
 ERROR: Unclocked write port 0 on memory top.ram.
Add model with memory block too, so you can cover line block starting at
line 419
2.dff2dffe -direct - skipped: ERROR: Found error in internal cell
\dffe.$procdff$47 ($dffe) at
3.insbuf -buf $_BUF_ in out - skipped: ERROR: Found error in internal
cell

5. clk2fflogic (104 - 144,180-195 are not covered)
9. memory_nordff(75-101 is not covered)
10. memory_unpack(91-108 is not covered)
12. hierarchy (the coverage from 44% increased to 61,3%)