Initial read-daemon for hwmon entries

Discoveres hwmon entries for fans, input voltage, and temperature
sensors.  Polls entries on a 1s interval and displays a message to
stdout if one of the entries have changed.
diff --git a/sensorset.C b/sensorset.C
new file mode 100644
index 0000000..8b59ac1
--- /dev/null
+++ b/sensorset.C
@@ -0,0 +1,26 @@
+#include <regex>
+#include <iostream>
+#include "sensorset.H"
+#include "directory.H"
+
+// TODO: Issue#2 - STL regex generates really bloated code.  Use POSIX regex
+//       interfaces instead.
+static const std::regex sensors_regex =
+    std::regex("^(fan|in|temp)([0-9]+)_([a-z]*)", std::regex::extended);
+static const auto sensor_regex_match_count = 4;
+
+SensorSet::SensorSet(const std::string& path)
+{
+    Directory d(path);
+    std::string file;
+
+    while(d.next(file))
+    {
+        std::smatch match;
+        std::regex_search(file, match, sensors_regex);
+
+        if (match.size() != sensor_regex_match_count) continue;
+
+        container[make_pair(match[1],match[2])].emplace(match[3]);
+    }
+}