Set hlv consistent with ESM1.6 UM and CICE

[blimlim]

Description
This pull request updates the value for the latent heat of evaporation from 2.50e6 J/kg to 2.501e6 J/kg. This is done for consistency with the values used in UM and CICE in ESM1.6, and the change results in an improvement in the coupled model's water balance.

Closes #17

How Has This Been Tested?
This change has been tested in a 3 month run of ESM1.6. It results in no loss of water during the evaporation coupling:

Compared to a loss of ~6.3e6kg/s without the change:

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes

[dougiesquire]

Thanks @blimlim! Could you please add comments to the code noting that HLV has been changed and why

[blimlim]

Could you please add comments to the code noting that HLV has been changed and why

Good idea! I've added some comments in 47288ff

[dougiesquire]

Sorry, being unnecessarily persnickety

[dougiesquire]

Thanks @blimlim! Please "squash and merge"

[blimlim]

Thanks @dougiesquire!