Add fixes for imphash calculation

[secDre4mer]

Add some fixes where the imphash was calculated incorrectly:

• Upper case DLL extensions were not removed
• Missing DLL extensions could cause a panic
• Ordinal lookups weren't functioning correctly

Add test cases (based on the existing files) that ensure correct functionality.

[codecov]

Codecov Report

Merging #17 (5a752c2) into main (29aec65) will increase coverage by 1.05%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main      #17      +/-   ##
==========================================
+ Coverage   38.94%   40.00%   +1.05%     
==========================================
  Files          25       25              
  Lines        3425     3427       +2     
==========================================
+ Hits         1334     1371      +37     
+ Misses       1886     1844      -42     
- Partials      205      212       +7     

Impacted Files	Coverage Δ
imports.go	59.28% <50.00%> (+5.36%)	⬆️
debug.go	30.43% <0.00%> (+6.76%)	⬆️
ordlookup.go	57.14% <0.00%> (+57.14%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 29aec65...5a752c2. Read the comment docs.

[LordNoteworthy]

Thanks a lot @secDre4mer for those commits, looking good. I have created a new tag that contains this fix.