publishes digital input port state

[at-wat]

No description provided.

[at-wat]

tested with TF-2MD3

[at-wat]

commands

$ rosrun ypspur_ros ypspur_ros _param_file:=PARAM_FILE _dio7_enable:=true _dio7_input:=true _dio7_name:=test1 _dio0_enable:=true _dio0_name:=test0 _dio0_output:=false _dio0_intput:=true

$ rostopic echo /ypspur_ros/digital_input

$ rostopic pub /ypspur_ros/test1 ypspur_ros/DigitalOutput "output: 1
toggle_time:
  secs: 2
  nsecs: 0" 

results

header: 
  seq: 7065
  stamp: 
    secs: 1481547851
    nsecs: 586544699
  frame_id: ''
name: ['test0', 'test1']
state: [True, True]
---
header: 
  seq: 7066
  stamp: 
    secs: 1481547851
    nsecs: 591538319
  frame_id: ''
name: ['test0', 'test1']
state: [True, False]
---

The port state change had been detected. It is also confirmed that it worked with shorting io ports with GND.

[at-wat]

This fixes #5.