STYLE: Prefer error checked std::sto[id] over ato[if].
STYLE: Prefer error checked std::sto[id] over ato[if].

The `ato[if]` functions do not provide mechanisms for distinguishing
between `0` and the error condition where the input can not be converted.

`std::sto[id]` provides exception handling and detects when an invalid
string attempts to be converted to an [integer|double].

`ato[if]()`
 - **Con**: No error handling.
 - **Con**: Handle neither hexadecimal nor octal.

The use of `ato[if]` in code can cause it to be subtly broken.
`ato[if]` makes two very big assumptions indeed:
 - The string represents an integer/floating point value.
 - The integer can fit into an int.

In agreement with:
http://review.source.kitware.com/#/c/23738/

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