use make_shared wherever possible

[mlautman]

Quoting @tylerjw

For exception safety, memory leak avoidance, and performance reasons (one call to malloc instead of two) always use make_shared instead of new.

Also, when using make shared to create a new local variable use auto because the type is already represented in the template for make_shared and putting it at the start of the line does not add any more useful information or make the code more readable.

Reference: https://stackoverflow.com/questions/14836691/is-it-better-to-use-shared-ptr-reset-or-operator