Rename shell runner and debugger -> mojo_run, mojo_debug.

mojo/devtools/common/README.md

 # Devtools
 
 Unopinionated tools for **running**, **debugging** and **testing** Mojo apps.
 
 ## Install
 
 ```
 git clone https://github.com/domokit/devtools.git
 ```
 
 ## Contents
 
 Devtools offers the following tools:
 
- - `mojo_shell` - universal shell runner
- - `debugger` - supports interactive tracing and debugging of a running mojo
+ - `mojo_run` - universal shell runner
+ - `mojo_debug` - supports interactive tracing and debugging of a running mojo
    shell
  - `remote_adb_setup` - configures adb on a remote machine to communicate with
    a device attached to the local machine
 
 and a Python scripting library designed for being embedded (`devtoolslib`).
 
-### debugger
+### Debugger
 
-The `debugger` script allows you to interactively inspect a running shell,
+The `mojo_debug` script allows you to interactively inspect a running shell,
 collect performance traces and attach a gdb debugger.
 
 #### Tracing
 To collect [performance
 traces](https://www.chromium.org/developers/how-tos/trace-event-profiling-tool)
 and retrieve the result:
 
 ```sh
-debugger tracing start
-debugger tracing stop [result.json]
+mojo_debug tracing start
+mojo_debug tracing stop [result.json]
 ```
 
 The trace file can be then loaded using the trace viewer in Chrome available at
 `about://tracing`.
 
 #### GDB
 It is possible to inspect a Mojo Shell process using GDB. The `debugger` script
 can be used to launch GDB and attach it to a running shell process (android
 only):
 
 ```sh
-debugger gdb attach
+mojo_debug gdb attach
 ```
 
 #### Android crash stacks
 When Mojo shell crashes on Android ("Unfortunately, Mojo shell has stopped.")
 due to a crash in native code, `debugger` can be used to find and symbolize the
 stack trace present in the device log:
 
 ```sh
-debugger device stack
+mojo_debug device stack
 ```
 
 ### devtoolslib
 
 **devtoolslib** is a Python module containing the core scripting functionality
 for running Mojo apps: shell abstraction with implementations for Android and
 Linux and support for apptest frameworks. The executable scripts in devtools are
 based on this module. One can also choose to embed the functionality provided by
 **devtoolslib** in their own wrapper.
 
 ## Development
 
 The library is canonically developed [in the mojo
 repository](https://github.com/domokit/mojo/tree/master/mojo/devtools/common),
 https://github.com/domokit/devtools is a mirror allowing to consume it
 separately.