simplified the function to load context files; extract the part to load single context files, etc.
rename the function to get site ctx file[s] from site_src_ctxs to site_src_ctx as it returns a string not a list of strings in miniascape.globals
fix a bug that 'topdir' argument not passed to site_confdir from site_src_ctx in miniascape.globals
add some more test cases to test behavior of miniascape.options.tweak_options
do not set options.site if options.ctx was given; it may be set from ctx
follow changes in miniascape.options.tweak_options