Add autobuild build files

Pipfile

+[[source]]
+url = "https://pypi.org/simple"
+verify_ssl = true
+name = "pypi"
+
+[dev-packages]
+
+[packages]
+llbase = "*"
+certifi = "*"
+autobuild = {hg = "https://bitbucket.org/alchemyviewer/autobuild-1.1"}
+
+[requires]
+python_version = "2.7"

autobuild.xml

+<?xml version="1.0" ?>
+<llsd>
+<map>
+    <key>package_description</key>
+    <map>
+      <key>canonical_repo</key>
+      <string>https://bitbucket.org/alchemyviewer/3p-modernjson</string>
+      <key>copyright</key>
+      <string>Copyright (c) 2013-2019 Niels Lohmann</string>
+      <key>description</key>
+      <string>JSON for Modern C++</string>
+      <key>license</key>
+      <string>MIT</string>
+      <key>license_file</key>
+      <string>LICENSES/modernjson.txt</string>
+      <key>name</key>
+      <string>modernjson</string>
+      <key>platforms</key>
+      <map>
+        <key>common</key>
+        <map>
+          <key>build_directory</key>
+          <string>stage</string>
+          <key>configurations</key>
+          <map>
+            <key>Release</key>
+            <map>
+              <key>build</key>
+              <map>
+                <key>arguments</key>
+                <array>
+                  <string>-c</string>
+                  <string>../build-cmd.sh</string>
+                </array>
+                <key>command</key>
+                <string>bash</string>
+              </map>
+              <key>default</key>
+              <boolean>true</boolean>
+              <key>name</key>
+              <string>Release</string>
+            </map>
+          </map>
+          <key>manifest</key>
+          <array>
+            <string>LICENSES/modernjson.txt</string>
+            <string>include/nlohmann/*</string>
+          </array>
+          <key>name</key>
+          <string>common</string>
+        </map>
+      </map>
+      <key>source_directory</key>
+      <string>json</string>
+      <key>version_file</key>
+      <string>VERSION.txt</string>
+    </map>
+    <key>type</key>
+    <string>autobuild</string>
+    <key>version</key>
+    <string>1.3</string>
+  </map>
+</llsd>

build-cmd.sh

+#!/usr/bin/env bash
+
+cd "$(dirname "$0")"
+
+# turn on verbose debugging output for parabuild logs.
+exec 4>&1; export BASH_XTRACEFD=4; set -x
+# make errors fatal
+set -e
+# complain about unset env variables
+set -u
+
+if [ -z "$AUTOBUILD" ] ; then 
+    exit 1
+fi
+
+if [ "$OSTYPE" = "cygwin" ] ; then
+    autobuild="$(cygpath -u $AUTOBUILD)"
+else
+    autobuild="$AUTOBUILD"
+fi
+
+top="$(pwd)"
+stage="$(pwd)/stage"
+
+mkdir -p $stage
+
+# Load autobuild provided shell functions and variables
+source_environment_tempfile="$stage/source_environment.sh"
+"$autobuild" source_environment > "$source_environment_tempfile"
+. "$source_environment_tempfile"
+
+NLOHMANNJSON_SOURCE_DIR="json"
+
+build=${AUTOBUILD_BUILD_ID:=0}
+
+# Create the staging folders
+mkdir -p "$stage/include/nlohmann"
+
+pushd "$NLOHMANNJSON_SOURCE_DIR"
+    case "$AUTOBUILD_PLATFORM" in
+        common*)
+            cp -a include/nlohmann/* "$stage/include/nlohmann"
+
+            VERSION_HEADER_FILE="include/nlohmann/json.hpp"
+            version_major=$(sed -n -E 's/#define NLOHMANN_JSON_VERSION_MAJOR ([a-z0-9.]+)/\1/p' "${VERSION_HEADER_FILE}")
+            version_minor=$(sed -n -E 's/#define NLOHMANN_JSON_VERSION_MINOR ([a-z0-9.]+)/\1/p' "${VERSION_HEADER_FILE}")
+            version_patch=$(sed -n -E 's/#define NLOHMANN_JSON_VERSION_PATCH ([a-z0-9.]+)/\1/p' "${VERSION_HEADER_FILE}")
+            echo "${version_major}.${version_minor}.${version_patch}.${build}" > "${stage}/VERSION.txt"
+        ;;
+    esac
+    mkdir -p "$stage/LICENSES"
+    cp LICENSE.MIT "$stage/LICENSES/modernjson.txt"
+popd