Crossover extraction using PyReX

Along track data (individual track files) with three columns (lon, lat, z) in ASCII format (.txt, .dat) should be placed in input folder. Two sample datasets (group_a and group_b) containing the along track (ship borne) free-air gravity from NGDC is already present in the input folder.
The output of PyReX will be saved in the folder output_detection_files. Make a folder if it doesn't exist.
Config script config_cross.py along with detection.py, correction.py, stacking.py and a module file cross_over_module.py are placed in codes folder.

To run the detection:

Go to codes folder
```
$ cd codes
```
Users can modify the config_cross.py as per the requirement. The config_cross.py script is already set to run detection from files in input folder.
config_cross.py has sections with pyrex_group_a_detect and pyrex_group_b_detect as calc_id.
Run the detection for Group A with its corresponding calc_id
```
$ python detection.py pyrex_group_a_detect
```
Similarly, run the detection for Group B with its corresponding calc_id
```
$ python detection.py pyrex_group_b_detect
```
Extracted crossovers are present in output_detection_files folder and named corresponding to their calc_id.

Auxillary codes

Similarly, correction.py and stacking.py can be run by adding corresponding sections in config_cross.py as

$ python stacking.py stacking_calc_id

for stacking and

$ python correction.py corrections_calc_id

for corrections.