LSan: "LSAN_OPTIONS" docs should be updated to be clearer on valid inputs

[mchristoff]

Currently, the LeakSanitizer documentation page is pretty sparse on the specifics of "LSAN_OPTIONS" syntax:
https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer

It took me quite a while to figure out that the only way to have spaces in the "LSAN_OPTIONS" environment variable was to use single (not double) quotes. This limitation isn't very well documented, though it should be.
i.e.
setenv LSAN_OPTIONS "suppressions='/tmp/white space/lsan_suppress'" works but
setenv LSAN_OPTIONS "suppressions=/tmp/white space/lsan_suppress" or
setenv LSAN_OPTIONS "suppressions=\"/tmp/white space/lsan_suppress\"" don't work.

Including an example of multiple flags being added to the "LSAN_OPTIONS" environment variable would also be helpful:
setenv LSAN_OPTIONS "allocator_may_return_null=1:suppressions=/tmp/lsan_suppress"

I would note that this can also apply to all the other "*_OPTIONS" variables for the other sanitizers.