* common.cc,diskio.cc: Display units in "SI" as per https://github.com/brndnmtthws/conky/issues/86 request
* Make the mem* and swap* variables to accept additional argument to print the usage in SI units
* common.cc: Fix indentation
* core.cc: Make the strndup() function call as manifest constant
* Add two more formal parameters to "human_readable()"
* diskio.cc: Restore the multiply of 1024LL
* Move the base multiplying into standalone function
* Use the "apply_base_multiplier()" function where necessary