Revert "Add a placeholder for nucleo-64 boards.  Currently these are in various directories nucleo-f303re, nucleo-f334r8, and nucleo-l476rg but need to be consolidated here because these are all the same boards."

This reverts commit 935cc4e3.

Add a placeholder for nucleo-64 boards.  Currently these are in various directories nucleo-f303re, nucleo-f334r8, and nucleo-l476rg but need to be consolidated here because these are all the same boards.

Add configuration to prevent selection of Windows native toolchains when using Ubuntu under Windows 10

Back out most of 34be3e7c and update README again.  Windows native tools cannot be used with Ubuntu under Windows 10 now.  For Cygwin, that support depends on the 'cygpath -w' tool to convert POSIX paths to Windows paths.  There is no corresponding tool for Ubuntu under Windows 10.

Revert "sam_tc_clockselect() reworked to calculate frequency error using smallest possible divisor minimizing the frequency error rather than largest possible divisor which maximized the error."

This reverts commit 5d5851a5.

sam_tc_clockselect() reworked to calculate frequency error using smallest possible divisor minimizing the frequency error rather than largest possible divisor which maximized the error.