Modules: Restructured parsing code.

Module can now return a json_t object from rpi_module_get_value_t, and it will get parsed in REST api urls.

Signed-off-by: matematik7 <domen.ipavec@z-v.si>
Memory: Added two comments.

Signed-off-by: matematik7 <domen.ipavec@z-v.si>
Memory: Removed unnecessary struct.

Signed-off-by: matematik7 <domen.ipavec@z-v.si>
Memory: Fixed return of parse_meminfo_entry on failure.

Signed-off-by: matematik7 <domen.ipavec@z-v.si>
Modules: Fix bug in construct_full_json.

Signed-off-by: matematik7 <domen.ipavec@z-v.si>
Cpu: Created cpu module.

Signed-off-by: matematik7 <domen.ipavec@z-v.si>