misc. and install notes

INSTALL.md

@@ -0,0 +1,40 @@
+### Run-Time Compatibility
+
+Functions are provided to check the library configuration and solid harmonics orderings at runtime:
+
+Note: As of v2.8.0 (libtool-based), the configuration_accessor() function will return `(nyi)` by default.
+  Packagers are encouraged to patch a generated configuration string into file `configuration.cc` to
+  imitate future cmake-based behavior.
+
+```
+libint2::initialize();
+printf("SHGShell: %d\n", libint2::solid_harmonics_ordering());
+libint2::set_solid_harmonics_ordering(libint2::SHGShellOrdering_Gaussian);
+printf("SHGShell: %d\n", libint2::solid_harmonics_ordering());
+printf("Configuration: %s\n", libint2::configuration_accessor().c_str());
+libint2::finalize();
+```
+```
+SHGShell: 1
+SHGShell: 2
+Configuration: eri_c4_d0_l2;eri_c4_d0_l3;sss;...
+```
+
+For the C library, a similar function is available:
+
+```
+printf("CMake Configuration (C)  : %s\n", configuration_accessor());
+```
+```
+CMake Configuration (C)  : eri_c4_d0_l2;eri_c4_d0_l3;sss;...
+```
+
+If you have a built libint2 library whose history you don't know, a command like this on Linux can provide the same information:
+
+```
+strings -n80 /a/random/L2/lying/around/libint2.so
+```
+```
+eri_c2_d0_l2;eri_c2_d0_l3;eri_c2_d1_l2;eri_c3_d0_l2;eri_c3_d0_l3;eri_c3_d1_l2;eri_c4_d0_l2;eri_c4_d1_l2;impure_sh;onebody_d0_l2;onebody_d0_l3;onebody_d1_l2;sss
+```
+

include/libint2/numeric.h

@@ -10,6 +10,7 @@
 #include <limits>
 #include <sstream>
 #include <type_traits>
+#include <cmath>
 
 #if LIBINT_HAS_MPFR
 # include <cstddef>
@@ -56,10 +57,12 @@
    mpf_clear(x_to_a);
    return result;
  }
+#ifndef _MSC_VER
  /// this is needed to avoid ambiguity in pow(2.0, 2) ... the above pow competes with standard double pow(double, double)
  inline double pow(double x, int a) {
    return std::pow(x, static_cast<double>(a));
  }
+#endif
  /// implement erf for mpf_class using MPFR ... I do not claim to know what issues the rounding presents here
  inline mpf_class erf(mpf_class x) {
    const auto prec = x.get_prec();