First post-processing functions

Some functions to post-process LaMEM models. Plotting functions are in progress.

Author: TatjanaWeiler

docs/src/man/lamem_post_processing.md

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+# Post processing of numerical models
+
+To evaluate and analyse numerical simulations, we provide a few routines to make it easier to extract the dataset information. 
+
+
+```@docs
+get_phase
+get_phase_bool
+search_for_phase_properties
+get_data_timestep
+split_at__to_type
+search_for_model_constrains
+track_point_over_time
+deserialize_file
+```

docs/src/man/tutorial_lamem_post_processing.md

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+# Post processing of LaMEM files
+
+## Goal
+This tutorial visualizes how to do comparative analysis and quantitative evaluation of LaMEM models. The post-processing is julia based and extracts the information directly from the .pvtr-file. 
+
+
+## Steps
+
+## 1. Get general information
+Before beginning the post-processing, it is useful to extract some general information about the model. This includes material properties of the different phases, time of the time step, ascii-file stored information and the model data. 
+
+
+```julia
+using GeophysicalModelGenerator, LaMEM, Serialization
+
+#### set path and variables
+dat_path = ("../test/test_files/Subduction_VEP.dat")
+model_path = ("../test/test_files/timestep/")
+model_name = "VEP"
+timestep = "Timestep_00000000_0.00000000e+00"
+FileName_pvtr = "output.pvtr"
+p_fields = ["phase", "temperature"]
+output_dir = model_path
+
+# extract data information from ascii file
+surface_level = search_for_model_constrains(dat_path, "surf_level")
+
+# read output file
+material_block = Dict{String, Dict{String, Dict{String, String}}}()  # Dictionary to store material properties
+material_block = search_for_phase_properties(dat_path, model_name, "<MaterialStart>", "<MaterialEnd>")
+
+# get the time as a float number
+time = split_at__to_type([timestep],3,"Float")
+
+
+# extract data information for selected fields
+data = get_data_timestep(model_path,timestep,FileName_pvtr,p_fields,surface_level,false)
+```
+
+## 2. Start post-processing
+To analyse the differences between models and its evolution, coordinates of specific phases can be obtained either as a vector or as a matrix. Additionally, a point can be tracked over time for specific fields. 
+
+
+```julia
+# get information about where the phase is located
+processing_folder = joinpath(model_path,timestep)
+path = replace(processing_folder,"\\" => "/")*"/"
+indices = get_phase(path,FileName_pvtr,[2],false)
+matrix = get_phase_bool(path,FileName_pvtr,indices)
+
+# track one point over time
+name = "track"*string(indices[1])
+track_point = track_point_over_time(indices[1],p_fields,model_name,model_path,surface_level,name,output_dir,false)
+
+tracked_point = deserialize_file(output_dir,name)
+```
+
+
+
+
+If you want to run the entire example, you can find the .jl code [here](https://github.com/JuliaGeodynamics/GeophysicalModelGenerator.jl/blob/main/tutorial/Tutorial_post_processing.jl)