time_volume: Time-volume function
In dayvayen/commspacetime: Modeling Communication Space-Time For Acoustic Species

The last function in the series of modeling commmunication space-time.

1	time_volume(duration, rate, radius, sphere = T)

`duration`	How long each vocalization lasts for (seconds)
`rate`	How often each vocalization is produced per minute
`radius`	Calculated from the radius_calc.r function–radius of the sphere
`sphere`	If the vocalization is produced above the ground, this is set to true. If it's produced on the ground, it's set to false.