Restructured src/system/* files.

[NEW] Add src/system/require.lua.
[NOW] Now initialize nexus.core functions in conf.lua.
[MOD] Merge src/system/compress and src/system/serialize to
src/system/save.
[MOD] Merge src/system/decompress and src/system/deserialize to
src/system/load.
[DEL] Remove src/system/dump.lua.
[DEL] Remove src/system/profiler.lua.
[DEL] Remove src/system/updater.lua.