create_imu: Internal IMU Object Construction
In SMAC-Group/gmwm: Generalized Method of Wavelet Moments

Internal quick build for imu object.

1 2	create_imu(data, ngyros, nacces, axis, freq, unit = NULL, name = NULL, stype = NULL)

`data`	A `matrix` with dimensions N x length(index)
`ngyros`	An `integer` containing the number of gyroscopes
`axis`	A `vector` unique representation of elements e.g. x,y,z or x,y or x.
`freq`	An `integer` that provides the frequency for the data.
`unit`	A `string` that contains the unit expression of the frequency. Default value is `NULL`.
`name`	A `string` that provides an identifier to the data. Default value is `NULL`.
`stype`	A `string` that describes the sensor type. Default value is `NULL`.
`naccess`	An `integer` containing the number of accelerometers