add changelog file

CHANGELOG.md

+**2.0**
+
+*Updates:*
+
+* update of architecture of services
+* update of DB scheme
+* standardisation of names and methods
+* scales and xi converter modules now process and full-kinematic dependent
+* propagation of kinematics and GPD types to integration routines
+* comparison methods updated
+
+*Bug fixes:*
+
+* smart pointers
+* minor memory leaks corrected
+* problem with calling GPD evolution fixed
+* dispersion relation subtraction constant
+* memory leak in threads corrected
+
+*Features:*
+
+* new printing
+* possibility to run computations with only specific GPD types
+* units
+* code comments
+* possibility to set database server port via properties file
+
+*Physics:*
+
+* addition of new exclusive production channel - TCS
+* neural network library added
+* DVCS CCF module added based on recent neural network analysis
+* unused stuff removed
+* new GPD module for a selection of single parton type
+
+------
+
+**1.0**
+
+*Initial version*
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