Break out the assert macros in eunit.hrl to stdlib/include/assert.hrl

Several people have requested that the assert macros in EUnit should be
moved out to a separate header file. This patch puts them in
stdlib/include/assert.hrl, which gets included by the eunit.hrl file. Thus,
nothing changes for eunit users, but the asserts can now also be included
separately.
Merge branch 'dg/win_icon' into master-pu
Merge branch 'jd/file-ram-opt-doc' into master-pu
Merge branch 'avi/fix-os-cmd-win' into master-pu
Merge branch 'sk/odbc64' into master-pu
Merge branch 'kp/odbc-empty-params' into master-pu
Merge branch 'sal/ftp' into master-pu
Merge branch 'jv/cover-patches/OTP-10778' into master-pu
Merge branch 'as/tls-psk-srp-suites' into master-pu
Merge branch 'mh/duplicate_name_error_message' into master-pu
Merge branch 'rc/break-out-asserts' into master-pu