0.3.0

Changes:
Added existing namecheck when creating files
Lots of static analysis bugs #6
Added rename func
Fix SPIFFS_read length when reading beyond file size
Added reading beyond file length testcase
Made build a bit more configurable
Changed name in spiffs from "errno" to "err_code" due to conflicts compiling
in mingw
Improved GC checks, fixed an append bug, more robust truncate for very special
case
GC checks preempts GC, truncate even less picky
Struct alignment needed for some targets, define in spiffs config #10
Spiffs filesystem magic, definable in config

New config defines:
SPIFFS_USE_MAGIC - enable or disable magic check upon mount
SPIFFS_ALIGNED_OBJECT_INDEX_TABLES - alignment for certain targets
New API functions:
SPIFFS_rename - rename files
SPIFFS_clearerr - clears last errno
SPIFFS_info - returns info on used and total bytes in fs
SPIFFS_format - formats the filesystem
SPIFFS_mounted - checks if filesystem is mounted