Feature: Add MPI wrappers

[rouson]

Fixes #84

Prerequisite: fpm 0.10.1 to avoid unnecessary build repetition (see fortran-lang/fpm#1007).

To Do

• Facilitate both serial builds and MPI-enabled parallel builds

As of commit b17c2c0, executing the following command

fpm test --compiler mpifort --runner "mpiexec -n 1"

passes all tests only if the changes below are applied. However, applying these changes breaks serial builds with fpm test.

 % git diff
diff --git a/test/command_line_test.F90 b/test/command_line_test.F90
index 01b80c9e..cc7a7b30 100644
--- a/test/command_line_test.F90
+++ b/test/command_line_test.F90
@@ -56,7 +56,7 @@ contains
     character(len=132) command_message
 
     call execute_command_line( &
-      command = "fpm run --example get-flag-value -- --input-file some_file_name", &
+      command = "fpm run --example get-flag-value --compiler mpifort --runner 'mpiexec -n 1' -- --input-file some_file_name", &
       wait = .true., exitstat = exit_status, cmdstat = command_status, cmdmsg = command_message &
     )   
     test_passes = exit_status == 0 
@@ -68,7 +68,7 @@ contains
     character(len=132) command_message
 
     call execute_command_line( &
-      command = "fpm run --example handle-missing-flag -- --empty-flag", &
+      command = "fpm run --example handle-missing-flag --compiler mpifort --runner 'mpiexec -n 1' -- --empty-flag", &
       wait = .true., exitstat = exit_status, cmdstat = command_status, cmdmsg = command_message &
     )   
     test_passes = exit_status == 0 
@@ -80,7 +80,7 @@ contains
     character(len=132) command_message
 
     call execute_command_line( &
-      command = "fpm run --example check-command-line-argument -- --some-argument", &
+      command = "fpm run --example check-command-line-argument --compiler mpifort --runner 'mpiexec -n 1' -- --some-argument", &
       wait = .true., exitstat = exit_status, cmdstat = command_status, cmdmsg = command_message &
     )
     test_passes = exit_status == 0

[ktras]

@rouson What version of mpifort were you using? I can't get this branch to compile. Did you make any other local changes (other than what is in the comment related to testing) that aren't represented in the remote branch?