Fix "missing declaration for symbol ''pj_get_errno''"

[rtsisyk]

Closes #11

[Totktonada]

As I see the reason of the problem is the typo in pj_get_errno_ref() function name and it can be fixed in this way:

diff --git a/gis/projection.lua b/gis/projection.lua
index c11729e..1bd184f 100644
--- a/gis/projection.lua
+++ b/gis/projection.lua
@@ -41,7 +41,7 @@ projections.PROJ_VERSION = PROJ_VERSION
 
 local function ctx_raise()
     -- local errno = lib.pj_ctx_get_errno(ctx)
-    local errno = lib.pj_get_errno(ctx)
+    local errno = lib.pj_get_errno_ref()[0]
     error('PROJ: '..ffi.string(lib.pj_strerrno(errno)))
 end
 

@rtsisyk Can you please explain why do you choose to use pj_ctx_alloc() and related functions? Is thread safety matters in case of tarantool?

[rtsisyk]

@rtsisyk Can you please explain why do you choose to use pj_ctx_alloc() and related functions? Is thread safety matters in case of tarantool?

Because other API was marked as deprecated.

[Totktonada]

Because other API was marked as deprecated.

The whole proj_api.h is now deprecated. Anyway, both variants work, so I don't have objections.