Gas proper names

Ideally, all Xgases should include their proper name in the long_name attribute, rather than just its abbreviation. This section allows you to map the formula (e.g., "co2") to the proper name (e.g., "carbon dioxide"), e.g.:

[gas_long_names]
co2 = "carbon dioxide"
ch4 = "methane"
co = "carbon monoxide"

Note that the keys are the gases, not Xgases. A default list is included if not turned off in the [Defaults] section. See the source code for DEFAULT_GAS_LONG_NAMES for the current list. You can override any of those without turning off the defaults; e.g., setting h2o = "dihydrogen monoxide" in this section will replace the default of "water".

Of course, when explicitly defining an Xgas to copy, you can write in the proper name as the gas_long value. The [gas_long_names] section is most useful for automatically discovered Xgases, but it can also be useful when defining multiple Xgas variables that refer to the same physical gas, as the standard TCCON configuration does with CO2.