Windows fix (#11)

Fix adapted from https://discourse.mc-stan.org/t/pkgbuild-compile-dll-on-previously-working-rstantools-based-package-fails-with-file-too-big-error/21938/16 to make package compile on my Win10 desktop. Only included the code for `configure.win` as changing the other files broke everything. 

* Updated configure.win and testing workflow to check if this breaks everything.

* Removed windows-fix from testing workflow.

.gitignore

@@ -56,5 +56,8 @@ inst/doc
 *.o
 *.so
 
+# Ignore large file generated by compilation
+src/rmot.dll
+
 # Bugged directory from snapshot package
 tests/testthat/_snaps

configure.win

@@ -3,3 +3,6 @@
 # Generated by rstantools.  Do not edit by hand.
 
 "${R_HOME}/bin${R_ARCH_BIN}/Rscript.exe" -e "rstantools::rstan_config()"
+
+# Add configuration needed for big object files
+echo "PKG_CXXFLAGS += -Wa,-mbig-obj" >> ./src/Makevars.win