nloptr 2.0.1

This is a release mainly for increasing direct compatibility with most user cases. In details, here is the list of changes that have been made:

• Update SystemRequirements description to make it clearer which minimal versions of cmake (>= 3.15.0) and nlopt (>= 2.7.0) are required (#100, @HenrikBengtsson).
• End configuration sooner and louder if cmake is missing when needed with clearer message (#103, @eddelbuettel).
• Ensure system-wide installation of cmake in the list of suggestions to install it when missing.
• Update GHA scripts to latest versions.
• Configure git to always use LF line endings for configure.ac file.
• Add CI for R-devel on Windows with Rtools42.
• Fix for compatibility with versions of R anterior to 4.0 (#111).
• Look for a cmake3 binary in the current path before cmake for increasing compatibility with most RHEL/CentOS users (#104, @bhogan-mitre @HenrikBengtsson).