Don't use colons in file system names (e.g. path_delay_cache/gowin/GW2AR-LV18QN88PC8:C) but allow in *part* names

[RossBencina]

Without this patch, git clone fails checkout on Windows because there are file paths containing colons:

Microsoft Windows [Version 10.0.19045.5965]
(c) Microsoft Corporation. All rights reserved.

F:\Share\pipelinec>git clone https://github.com/JulianKemmerer/PipelineC.git
Cloning into 'PipelineC'...
remote: Enumerating objects: 15757, done.
remote: Counting objects: 100% (2375/2375), done.
remote: Compressing objects: 100% (294/294), done.
remote: Total 15757 (delta 2252), reused 2088 (delta 2077), pack-reused 13382 (from 3)
Receiving objects: 100% (15757/15757), 78.78 MiB | 2.25 MiB/s, done.
Resolving deltas: 100% (9620/9620), done.
error: invalid path 'path_delay_cache/gowin/GW2AR-LV18QN88PC8:C/syn/BIN_OP_EQ_uint10_t_uint1_t.delay'
fatal: unable to checkout working tree
warning: Clone succeeded, but checkout failed.        
You can inspect what was checked out with 'git status'
and retry with 'git restore --source=HEAD :/'

This PR fixes the problem by:

1. Renaming the offending directory inside path_delay_cache to use an underscore instead of a colon.
2. When a part name contains a colon (part names are specified using the #pragma PART directive), the path_delay_cache loader code now replaces colons with underscores.

[RossBencina]

Note that I am not sure why the gowin part name contains the ":C" suffix in the first place. It does not show up in a superficial search. Perhaps it is the speed grade but that is just a guess.

[JulianKemmerer]

later there is a split( on colon in that gowin py file that I think needs to be changed to underscore? or another alternative safe to split on char chosen?

I think there is some discussion about why that might have been chosen arbitrarily kinda here where I say sounds reasonable because at the time it did sound that way 😏 #190 (comment)