* feat(mem): add initial version of tlsf
from : https://github.com/mattconte/tlsf
commit: deff9ab509341f264addbd3c8ada533678591905
* feat(mem): switch the default allocator to tlsf
* fix(mem): remove the preserved small buffer
since the builtin allocator(tlsf) is fast enough now
* fix(mem): change LV_MEM_ADD_JUNK to 0
to speed up the normal operation
* fix(style): remove the wrong first break statement from lv_style_prop_get_default
and correct the comment and style
* fix(style): handle the out of memory gracefully in lv_style_[set|remove]_prop
* fix(fs): don't allocate lv_fs_file_t in lv_fs_open
avoid the unnecessary allocation
* fix(fs): apply the similar file open/close change to dir open/close
avoid the unnecessary allocation
* fix(gc): remove the unused variables from gc
* fix(gc): correct typo(from _lv_img_defoder_ll to _lv_img_decoder_ll)
* fix(gc): change _lv_drv_ll to _lv_fsdrv_ll
since only instances fo lv_fs_drv_t can be added to this list
* fix(gc): Iterate the root variables only when they are really used
to save the memory space
* fix(image cache): move cache_temp to gc.h
and rename it to _lv_img_cache_single
* fix(mem): reutrn NULL in lv_mem_buf_get if allocation fail
* fix(mem): refine the loop in alloc_core to simplify the logic
* fix(mem): remove the lv_mem_buf declaration from lv_mem.h
since it already declared in gc.h
* fix(timer): remove LV_GC_INCLUDE inclusion since it doesn't need anymore
please see commit d6ca15a74923f2e86ce1e4ee6ee83bb2bbc887b8 for more info
* fix(timer): implement lv_timer_create directly
and call it in lv_timer_create_basic
* fix(timer): exclude the return value computing from the idle time
and change handler_start and time_till_next to local variables
* fix(timer): restart the timer process loop correctly
* fix(timer): skip the count pause timer into next timeout
it's wrong to check repeat_count since the timer is always
removed from the list once the repeat_count change to zero
* fix(timer): remove zero task_deleted and task_created in lv_task_exec
since the loop in lv_task_handler already do the same thing
