Changes in version 2.1.0 (2016-07-29)                  

    o   last_o2():	new function

    o   changed code to use measurements::conv_unit() rather than the defunct birk::conv_unit()

                 Changes in version 2.0.0 (2016-03-14)                  

    o   import_o2():		when multiple units of O2 are recorded, the notification has been downgraded from a warning to a message.

    o   import_o2():		improved speed

    o   o2_unit_conv():	MAJOR UPDATE: updated so that any O2 unit can be provided as an argument, not just percent air saturation. No longer backwards compatible with v1.0.0.

    o   o2_unit_conv():	added kPa, ml_per_l, mmHg, and inHg as unit options

                 Changes in version 1.0.0 (2015-02-11)                  

    o   import_o2():		new function

    o   o2_unit_conv():	new function