Add calibratable parameters to bmi_topmodel.c

[SnowHydrology]

Current behavior

TOPMODEL reads in parameter values from params.dat. If you want to change parameter values, you need to edit that file.

Expected behavior

A recent pull request in the ngen repo gives Nextgen the ability to change parameter values. This means we can use the model engine to override parameter values from params.dat. To do this, we'll need to edit bmi_topmodel.c to include calibratable parameters. We should follow the updated bmi_cfe.c file as a template: https://github.com/NOAA-OWP/cfe/blob/master/src/bmi_cfe.c

Steps to perform

1. Identify all parameters to add
2. Add #define PARAM_VAR_NAME_COUNT
3. Add static const char *param_var_names[PARAM_VAR_NAME_COUNT] and static const char *param_var_types[PARAM_VAR_NAME_COUNT]
4. Update static int Get_value_ptr to include all added parameters

Parameters to include

The following vars are included in params.dat (thanks @madMatchstick for the table!)

Variable	Datatype	Limits	Units	Role	Process	Description
subcat	char	256		info_string		character title of subcatment; often same as model title
szm	double		meters	parameter_fixed	rainfall-runoff	exponential scaling parameter for the decline of transmissivity with increase in storage deficit; units of depth
t0	double		ln(meters^2)	parameter_fixed		areal average of ln(a/tanB)
td	double		hours	parameter_adjustable	rainfall-runoff	unsaturated zone time delay per unit storage deficit
chv	double		meters/hour	parameter_fixed	overland flow	average channel flow velocity
rv	double		meters/hour	parameter_fixed	overland flow	internal overland flow routing velocity
srmax	double		meters	parameter_adjustable	rainfall-runoff	maximum root zone storage deficit
Q0	double		meters/hour	state		initial subsurface flow per unit area
sr0	double		meters	state		initial root zone storage deficit below field capacity
infex	int	Boolean		option	green-ampt	set to 1 to call subroutine to do infiltration excess calcs; not usually appropriate in catchments where Topmodel is applicable (shallow highly permeable soils); default to 0
xk0	double		meters/hour	parameter_adjustable	rainfall-runoff	surface soil hydraulic conductivity
hf	double		meters	parameter_adjustable	green-ampt	wetting front suction for G&A soln.
dth	double			parameter_adjustable	green-ampt	water content change across the wetting front; dimensionless

[SnowHydrology]

@xfeng2021, can you look at the table above and let me know which parameters you'd like added?

[xfeng2021]

I forwarded the table with the list of parameters to you. Thanks.

[hellkite500]

Also, a few more details on implementing/updating the BMI components can be found in NOAA-OWP/cfe#44

You can verbatim copy this commit content from these commits
NOAA-OWP/cfe@cacb838
NOAA-OWP/cfe@85ec486

Then just implement for the specific names these commits
NOAA-OWP/cfe@cd65034
NOAA-OWP/cfe@316f767

This assumes that set_value works similarly to CFE's set_value in which it uses get_value_ptr to implement the function. If it doesn't, adjust accordingly, but make sure that get_var_type is properly implemented for parameters you wish to expose this way.