refac(src): export everything via one module

This commit refactors the directory structure to support accessing
all currently public module entities via one common assert_m
module, which is in what is now the only file at the top level of
the src/ subdirectory: assert_m.F90.  All pre-existing files in
src/ have been  moved to the new src/assert subdirectory, a common
pattern employed across many projects.

Author: rouson

src/assert_m.F90 src/assert/assert_subroutine_m.F90src/assert_m.F90 renamed to src/assert/assert_subroutine_m.F90

@@ -4,7 +4,7 @@
 !     "Multi-Dimensional Physics Implementation into Fuel Analysis under Steady-state and Transients (FAST)",
 !     contract # NRC-HQ-60-17-C-0007
 !
-module assert_m
+module assert_subroutine_m
   !! summary: Utility for runtime checking of logical assertions.
   !! usage: error-terminate if the assertion fails:
   !!
@@ -44,4 +44,4 @@ pure module subroutine assert(assertion, description, diagnostic_data)
 
   end interface
 
-end module
+end module assert_subroutine_m

src/assert_s.f90 src/assert/assert_subroutine_s.f90src/assert_s.f90 renamed to src/assert/assert_subroutine_s.f90

@@ -4,7 +4,7 @@
 !     "Multi-Dimensional Physics Implementation into Fuel Analysis under Steady-state and Transients (FAST)",
 !     contract # NRC-HQ-60-17-C-0007
 !
-submodule(assert_m) assert_s
+submodule(assert_subroutine_m) assert_subroutine_s
   implicit none
 
 contains
@@ -84,4 +84,4 @@ end function string
 
   end procedure
 
-end submodule
+end submodule assert_subroutine_s

src/characterizable_m.f90 src/assert/characterizable_m.f90src/characterizable_m.f90 renamed to src/assert/characterizable_m.f90

@@ -0,0 +1,6 @@
+module assert_m
+  use intrinsic_array_m
+  use assert_subroutine_m
+  use characterizable_m
+  implicit none
+end module assert_m