Log Message:
Update libfilezilla to 0.5.3:

2016-06-20 - libfilezilla 0.5.3 released
New features:

    Add fz::replace_substrincs to search and replace substrings in std::(w)string

Bugfixes and minor changes:

    Explicitly request large file support on 32bit systems

2016-05-20 - libfilezilla 0.5.2 released
New features:

    Add fz::shared_optional::is_same that checks whether two instances share the \ 
same underlying pointer value, like a shallow equal.
    Add fz::int_to_hex_char as reverse to fz::hex_char_to_int

2016-05-09 - libfilezilla 0.5.1 released
New features:

    Add constructore to sparse_optional taking pointers

Bugfixes and minor changes:

    Fix compilation on systems where iconv's second argument is const