Add astc decoding - #3

Use ordinal string comparison (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1309)

Member 'LoadActualImage' does not access instance data and can be marked as static (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1822)

Member 'OpenCompare' does not access instance data and can be marked as static (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1822)

Member 'DecompressDds' does not access instance data and can be marked as static (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1822)

Exception type System.Exception is not sufficiently specific (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca2201)

Do not declare visible instance fields (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1051)

Do not declare visible instance fields (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1051)

Do not declare visible instance fields (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1051)

Do not declare visible instance fields (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/quality-rules/ca1051)