Raise exception in connect and element when failed

- The shell only generates an error message when an attempt to connect
two objects via message fails. This caused hard to debug errors. Now
the wrapper function raises RuntimeError in such case.

- `element(path)` returned the roor element when `path` does not
exist, again causing hard to find bugs. This now raises RuntimeError.

README.md

@@ -41,7 +41,7 @@ https://github.com/BhallaLab/moose-examples.
 # Build 
 
 To build `pymoose`, follow instructions given in
-[INSTALLATION.md](INSTALLATION.md) and for platform specific
+[INSTALLATION.md](INSTALL.md) and for platform specific
 information see:
 - Linux: [UbuntuBuild.md](UbuntuBuild.md)
 - MacOSX: [AppleM1Build.md](AppleM1Build.md)

python/moose/__init__.py

@@ -204,7 +204,10 @@ def connect(src, srcfield, dest, destfield, msgtype="Single"):
     """
     src = _moose.element(src)
     dest = _moose.element(dest)
-    return src.connect(srcfield, dest, destfield, msgtype)
+    msg = src.connect(srcfield, dest, destfield, msgtype)
+    if msg.name == '/':
+        raise RuntimeError(f'Could not connect {src}.{srcfield} with {dest}.{destfield}')
+    return msg
 
 
 def delete(arg):
@@ -239,6 +242,8 @@ def element(arg):
         MOOSE element (object) corresponding to the `arg` converted to write
         subclass.
     """
+    if not _moose.exists(arg):
+        raise RuntimeError(f'{arg}: element at path does not exist')
     return _moose.element(arg)