Enable threading when building for most platforms

Don't enable threading globally since the MSVC/ARM build target
(neither windows phone nor windows rt) doesn't support the normal
windows threading functions.
Remove spaces from the argument to LINK_LIB

In make on some platforms, this ended up as passing -l <lib>
with a space inbetween. This wasn't an error, but wasn't what
was intended either.
Merge the ls_defines.h headers into the common sub-library
Simplify the make rules for creating libraries
Remove an unused function for byte order swapping
Unify the fallback codepath for getting prefix bits into a macro

This avoids having to know the details about when the optimized
codepath is available at the place where it's used.
Simplify debugging code - always write debug trace files to the cur directory

This reduces the amount of platform ifdefs.
Remove the now meaningless field sTracePath
Consistently use the compat wrappers for file IO

As long as WelsFileHandle* is equal to FILE* this doesn't matter,
but for consistency use the WelsF* functions for all handles
opened by WelsFopen, and use WelsFileHandle* as type for it
instead of FILE*.
Removed an unused pair of files generated by MSVC project wizards

These files aren't actually even referenced by the MSVC project
files.
Merge pull request #241 from mstorsjo/remove-unused-function

Remove an unused function for byte order swapping
Merge pull request #243 from mstorsjo/use-stdio-wrappers

Consistently use the compat wrappers for file IO
Merge pull request #244 from mstorsjo/remove-unused-files

Removed an unused pair of files generated by MSVC project wizards
Merge pull request #242 from mstorsjo/simplify-debug-file-locations

Simplify debugging code by always writing trace files to the current directory
Merge pull request #240 from mstorsjo/simplify-inline-asm

Unify the fallback codepath for getting prefix bits into a macro
Merge pull request #237 from mstorsjo/simplify-make-lib-rules

Simplify the make rules for creating libraries
Merge pull request #235 from mstorsjo/merge-ls-defines

Merge the ls_defines.h headers into the common sub-library
Merge pull request #229 from mstorsjo/make-link-space

Remove spaces from the argument to LINK_LIB
Merge pull request #222 from mstorsjo/enable-threading

Enable threading when building for most platforms