Work harder to make a usable temporary directory for writing minidumps

Also document where the minidump file might be found in the manpage
Provide command line options for nodelete, noreport

Environment variables are actually of limited use as a Win32 process inherits a
very limited environment from a cygwin process, so provide command line switches
instead.

Quoting is now supported in the CYGWIN environment variable, so these can be
used there, e.g.

export CYGWIN='"error_start=C:\cygwin64\bin\cygwin-crashreporter-gui -r -k"'