Link to GTSAM-EXPORT doc

DEVELOP.md

@@ -17,3 +17,5 @@ class GTSAM_EXPORT MyClass { ... };
 
 GTSAM_EXPORT myFunction();
 ```
+
+More details [here](Using-GTSAM-EXPORT.md).

Using-GTSAM-EXPORT.md

@@ -10,7 +10,7 @@ To create a DLL in windows, the `GTSAM_EXPORT` keyword has been created and need
 3.  If you have defined a class using `GTSAM_EXPORT`, do not use `GTSAM_EXPORT` in any of its individual function declarations.  (Note that you _can_ put `GTSAM_EXPORT` in the definition of individual functions within a class as long as you don't put `GTSAM_EXPORT` in the class definition.)
 
 ## When is GTSAM_EXPORT being used incorrectly
-Unfortunately, using `GTSAM_EXPORT` incorrectly often does not cause a compiler or linker error in the library that is being compiled, but only when you try to use that DLL in a different library.  For example, an error in gtsam/base will often show up when compiling the check_base_program or the MATLAB wrapper, but not when compiling/linking gtsam itself.  The most common errors will say something like:
+Unfortunately, using `GTSAM_EXPORT` incorrectly often does not cause a compiler or linker error in the library that is being compiled, but only when you try to use that DLL in a different library.  For example, an error in `gtsam/base` will often show up when compiling the `check_base_program` or the MATLAB wrapper, but not when compiling/linking gtsam itself.  The most common errors will say something like:
 
 ```
 Error	LNK2019	unresolved external symbol "public: void __cdecl gtsam::SO3::print(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &)const " (?print@SO3@gtsam@@QEBAXAEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) referenced in function "public: static void __cdecl gtsam::Testable<class gtsam::SO3>::Print(class gtsam::SO3 const &,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &)" (?Print@?$Testable@VSO3@gtsam@@@gtsam@@SAXAEBVSO3@2@AEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z)	check_geometry_program	C:\AFIT\lib\gtsam\build\gtsam\geometry\tests\testSO3.obj