Log Message:
libfilezilla: update to 0.15.1.

0.15.1 (2018-11-22)

+ Add argument to fz::strtok to return empty tokens
- Fix compatibility issue with Nettle < 3.3
- Fix fz::random_bytes on MinGW
- Fix memory leak in fz::buffer

0.15.0 (2018-10-19)

+ libfilezilla now depends on Nettle >= 3.1
+ Added fz::sha512, fz::sha256, fz::sha1 and fz::md5 hash functions
+ Added fz::hash_accumulator
+ Added fz::hmac_sha256 HMAC function
+ Added asymmetric encryption scheme using X25519
+ Added signature scheme using Ed25519
- Changed and documented semantics of the return value of fz::remove_file, \ 
removing a non-existing file is not an error

0.14.0 (2018-10-04)

+ Added fz::equal_insensitive_ascii
+ Added insensitive_ascii parameter to fz::starts_with and fz::ends_with
- Fixed namespace of to_wstring in wx glue

0.13.2 (2018-09-21)

- Fix regression in fz::shared_value::clear
- Fix parsing of URIs without path

0.13.1 (2018-09-10)

+ Made fz::scoped_lock movable
- Fix a few compiler warnings