Fix bug #1

[kemen209]

Use stoi to get int type of motion_multiplier_

[frazierbaker]

What was the issue this was intended to fix?

[kemen209]

To avoid implicitly type conversion from double to int. I assume motion_multiplier_ is suppose to be type of int.

[tm132]

motion_multiplier_ is defined as an int in the header file, so stoi would be correct in this context.

However, we have this in the same file:

motion_multiplier_ = 1;    // TM32: an int?
[......]
double MissionParse::motion_multiplier() { return motion_multiplier_; }   // TM132: a double??

Should it be a double or should it be an int?

[kemen209]

According to the following , motion_multiplier should be int.

(1) src/simcontrol/SimControl.cpp
for (int i = 0; i < mp_->motion_multiplier(); i++) {

(2) ./docs/source/overview/xml-tags.rst
:  - ``motion_multiplier`` : set to an integer greater than or equal to 1.

And i made a followi-up commit to change the API to return type int.

And for the motion_multiplier in JSBSimModel.cpp, such as

double motion_multiplier = std::stod(info["motion_multiplier"]);

It's came from the JSBSimModel plugin's xml file, not part of Mission file, only for calculating dt_, just leave it that way for now (or we can fix that too).