Fix a linking problem by moving Stroke::save() and load() into header

[ghost]

The template member functions Stroke::save and Stroke::load get called
via the serialize() function generated by boost's macro
BOOST_SERIALIZATION_SPLIT_MEMBER() in gesture.h. Since the definitions
of save()/load() are only available in gesture.cc, the compiler may
produce two versions of Stroke::serialize() -- one with save()/load()
inlined in gesture.o and one with calls to save()/load() in all other
referencing translation units. Since the compiler inlined Stroke::save()
and Stroke::load(), it will not export them in gesture.o (which is
legitimate, since the code only requests an export of
Stroke::serialize). As a result, some orders of object files can fail to
link, when the linker picks the version of Stroke::serialize() that
would call save()/load() (which are not available separately) instead of
the version with these functions inlined.

Avoid relying on this compiler- and optimization-level dependent
behavior by moving the definition of template member functions
Stroke::save() and Stroke::load() into gesture.h. As a side-effect, that
change unifies code style, since all other classes have their ::save()
and ::load() definitions in header files, too.

These link failures surfaced when building on s390x with -march=zEC12 or
later, and can be reproduced on x86_64 with gcc parameters
--param max-inline-insns-auto=80 --param inline-min-speedup=2

Signed-off-by: Marius Hillenbrand mhillen@linux.ibm.com

[ghost]

@markdstjohn Thanks for merging my patch, and thank you for your work on easystroke!