AppendToFile write s to the end of filename.

EnsureDir creates directory if it doesnt exist.

FileExist check if path exist.

GetDir returns the program root directory.

OverwriteFile truncate filename and write s into it.

OverwriteFileBytes truncate filename and write b []bytes into it.

OverwriteFileValueIndent marshall v into indented json, then truncate the file filename and write the marshalled bytes into it.

FileWriter allows concurrent writes to a file.