Update time_val.hpp

Thanks for David Welton for spotting this.
Added support for BOOST 1.54.0
Merge branch 'master' of github.com:saleyn/utxx
Minor version correction (thanks to Dmitriy)
Add online variance algorithm

Add a numerically stable algorithm for the computation of the variance
(and the mean as well).
Format the code with 4-space tabulation
Merge pull request #2 from GHamrouni/master

Add online variance algorithm
atomic_value class added
file_reader modified to accept stdin
Symbol-based trie classes.

Squashed commit of the following:

commit 18a2d897da442c69d90124bdaa44ca6bf2816805
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Thu Jun 20 20:52:52 2013 -0400

    refactoring

commit d38d89040f879f4ac0388b9f5014333709e1b736
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Tue Jun 11 23:58:07 2013 -0400

    strie update fix - allow update with arbitrary data

commit 55bce9e2f792621ff0910a47f438317a04dadb26
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Thu Jun 6 20:26:38 2013 -0400

    s-trie method added - folding data through the key parts

commit c312ff1310a58a6bdb260627e0f89466c2a254f1
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Wed Jun 5 20:33:36 2013 -0400

    optional exact key matching methods added; refactoring & cleanup.

commit dd08509182359b0054d0cfa7a809dcf380653785
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Tue May 21 22:47:47 2013 -0400

    update method added to s-trie; minor fixes.

commit 39f13563e698cdbd1dad4110e78b9fa3e04d3fdf
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Sat May 18 21:03:05 2013 -0400

    minor fix and cleanup; test case added; mmap-based s-trie works!

commit 4a3b21add8179c5a2198c93b32c4115918699c68
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Thu May 16 23:47:42 2013 -0400

    memory-region based s-trie classes; work in progress

commit 0d081f500956d9b1c066f2ceb0c5dce075d4ed5a
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Wed May 15 23:48:14 2013 -0400

    strie refactoring - work in progress

commit a185342c72b07998a893f2103972cb9e33b9de9f
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Tue May 7 19:20:14 2013 -0400

    refactoring

commit 5837f658e23a93179be65fd24839d7cc7eab9495
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Tue May 7 00:30:26 2013 -0400

    refactoring

commit 5e485fb781c777d5f909e5478412dcb296fe0b27
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Sun May 5 23:53:18 2013 -0400

    symbol-based trie - experimental code, work in progress.
auxillary class to trace object instances added.
doxygen minor fixes
s-trie classes refactored to generic trie with persistency

Squashed commit of the following:

commit e65dfc6dae119867bbf6be07f73ec912bc4da952
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Mon Oct 28 22:59:26 2013 -0400

    cleanup - old strie implementation removed

commit 32e168630ed77c930eb0375c68019d53f4357bbb
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Tue Oct 8 13:04:23 2013 -0400

    persistent trie - minor fixes

commit 67353374160afc7657f9e99c8a7a1610986752ef
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Sun Oct 6 23:54:48 2013 -0400

    generic trie with persistency - fixes; all relevant tests passed.

commit 6d66f76a77064193b88d4d2db5d9171c6b8e4962
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Sat Oct 5 00:04:21 2013 -0400

    generic trie with persistency - wip

commit edcef1a7abf7f046a1c8e4a4d6a9e8106cb13de5
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Mon Sep 30 21:37:24 2013 -0400

    actrie fixes; test cases for ac-trie completed

commit 56aa288ff67d08c5f8b63aa351cb4dfeabd68374
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Fri Sep 27 23:44:24 2013 -0400

    ac-trie: mostly done, test passed in s-trie compatibility mode

commit 126839479400e958f760dd5abfb731859d403037
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Sun Sep 22 23:56:49 2013 -0400

    ac-trie: work in progress

commit 426434a94ee8ca0bd2f5792ed4647aa759367391
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Thu Sep 19 22:05:42 2013 -0400

    minor fixes

commit 4dd94ca7ff5476d7bdbceca3b40c37e62e5f2b55
Author: Dmitriy Kargapolov <dmitriy.kargapolov@gmail.com>
Date:   Thu Sep 19 21:29:51 2013 -0400

    s-trie major refactoring
minor cleanup and refactoring; optional demo progs added.