[Development] This commit is not merged upstream

Description
================================================================================

- Modify "config.log_level" in development environment
- Modify Guardfile
  - Add setting of tmux notification
    - ref. https://github.com/guard/guard/wiki/System-notifications
  - Change setting of rubocop notification
    - ref. https://github.com/yujinakayama/guard-rubocop#available-options
- Add gems to pry
  - pry-rails
    - Rails 3 pry initializer
    - https://github.com/pry/pry-rails
  - pry-doc
    - Provide MRI Core documentation and source code for the Pry REPL
    - https://github.com/pry/pry-doc
  - pry-byebug
    - Pry navigation commands via byebug
    - https://github.com/deivid-rodriguez/pry-byebug
  - pry-stack_explorer
    - Walk the stack in a Pry session
    - https://github.com/pry/pry-stack_explorer

Usage
================================================================================

Run "rails server"

Add the "binding.pry" in the source to add a breakpoint.
Execution will stop in the first statement after your "binding.pry".

Execution Commands
================================================================================

step: Step execution into the next line or method. Takes an optional numeric
argument to step multiple times.

next: Step over to the next line within the same frame. Also takes an optional
numeric argument to step multiple lines.

finish: Execute until current stack frame returns.

continue: Continue program execution and end the Pry session.

"s" is alias of "step"
"n" is alias of "next"
"f" is alias of "finish"
"c" is alias of "continue"

Breakpoints
================================================================================

You can set and adjust breakpoints directly from a Pry session using the
following commands:

break: Set a new breakpoint from a line number in the current file, a file and
line number, or a method. Pass an optional expression to create a conditional
breakpoint. Edit existing breakpoints via various flags.

Examples:

break SomeClass#run            # Break at the start of `SomeClass#run`.
break Foo#bar if baz?          # Break at `Foo#bar` only if `baz?`.
break app/models/user.rb:15    # Break at line 15 in user.rb.
break 14                       # Break at line 14 in the current file.

break --condition 4 x > 2      # Change condition on breakpoint #4 to 'x > 2'.
break --condition 3            # Remove the condition on breakpoint #3.

break --delete 5               # Delete breakpoint #5.
break --disable-all            # Disable all breakpoints.

break                          # List all breakpoints. (Same as `breakpoints`)
break --show 2                 # Show details about breakpoint #2.
Type break --help from a Pry session to see all available options.

breakpoints: List all defined breakpoints. Pass -v or --verbose to see the
source code around each breakpoint.