Added simple particle data map in particles.h

.clang-format

+---
+BasedOnStyle:  LLVM
+BreakConstructorInitializersBeforeComma: true
+ConstructorInitializerAllOnOneLineOrOnePerLine: true
+Cpp11BracedListStyle: true
+Standard: Cpp11
+#SpaceBeforeParens: ControlStatements
+SpaceAfterControlStatementKeyword: true
+PointerBindsToType: true
+IncludeBlocks:   Preserve
+UseTab:          Never
+ColumnLimit:     120
+NamespaceIndentation: Inner
+AlignConsecutiveAssignments: true
+...

.gitignore

+doc/docs/*

include/common_bench/particles.h

+#ifndef COMMON_BENCH_PARTICLES_HH
+#define COMMON_BENCH_PARTICLES_HH 1
+
+#include <map>
+
+namespace common_bench {
+
+  struct ParticleData {
+    int pdgCode;
+    int charge;
+    double mass;
+    // std::string name;
+  };
+
+  using ParticleMap = std::map<int, ParticleData>;
+
+  const ParticleMap particleMap = {
+      {          11, {          11,  -1,   0.000510998928 }},  // e-
+      {         -11, {         -11,   1,   0.000510998928 }},  // e+
+      {          13, {          13,  -1,   0.105658357    }},  // mu-
+      {         -13, {         -13,   1,   0.105658357    }},  // mu+
+      {          22, {          22,   0,   0.0            }},  // gamma
+      {         111, {         111,   0,   0.1349766      }},  // pi0
+      {         211, {         211,   1,   0.1395701      }},  // pi+
+      {        -211, {        -211,  -1,   0.1395701      }},  // pi-
+      {         130, {         130,   0,   0.49767        }},  // K_L^0
+      {         310, {         310,   0,   0.49767        }},  // K_S^0
+      {         321, {         321,   1,   0.49360        }},  // K^+
+      {        -321, {        -321,  -1,   0.49360        }},  // K^-
+      {        2212, {        2212,   1,   0.93827        }},  // p+
+      {       -2212, {       -2212,  -1,   0.93827        }},  // p~-
+      {        2112, {        2112,   0,   0.93957        }},  // n0
+      {  1000010020, {  1000010020,   1,   1.87561        }},  // 1000010020 Deuterium
+      {  1000010030, {  1000010030,   1,   2.80925        }},  // 1000010030 Tritium
+      {  1000020030, {  1000020030,   1,   2.80923        }},  // 1000020030 He3
+      {  1000020040, {  1000020040,   1,   3.72742        }},  // 1000020040 Alpha-(He4)
+  };
+
+} // namespace common_bench
+
+#endif