Change default build directories to repository-relative paths

[fumitoh]

Summary

Updated the Build-QuantLibDLL.ps1 script to use repository-relative paths for default build and install directories instead of hardcoded absolute paths, making the build process more portable and allowing users to inspect patched sources locally.

Key Changes

• Changed default InstallDir from C:\quantlib-build\install to install/ in the repository root
• Changed default TempDir from $env:TEMP\quantlib-dll-build to build/ in the repository root
• Updated parameter documentation to clarify the new defaults and explain that the build directory can be used to inspect patched sources
• Added a note to README.md explaining the new default behavior and where users can find the patched QuantLib sources after building

Implementation Details

• Used Join-Path (Split-Path $PSScriptRoot) to construct paths relative to the repository root
• This approach makes the script more portable across different machines and environments
• Users can now easily inspect the patched QuantLib sources at build\QuantLib-<version>\ after the build completes
• The change maintains backward compatibility by allowing users to override these defaults via parameters

https://claude.ai/code/session_01EVB6yo51Ug6uCWAPSfUgwz