Lexer in D

[Namespace]

With reserving of 60% of the file size in memory I get a big 
speed boost.

------------------------
Total time (ms): 17544.6
Repetitions    : 200
Sample mode    : 87 (121 ocurrences)
Median time    : 87.3835
Avg time       : 87.7232
Std dev.       : 1.77905
Minimum        : 84.238
Maximum        : 101.919
95% conf.int.  : [84.2363, 91.21]  e = 3.48687
99% conf.int.  : [83.1407, 92.3057]  e = 4.58252
EstimatedAvg95%: [87.4766, 87.9697]  e = 0.246559
EstimatedAvg99%: [87.3991, 88.0472]  e = 0.324033

But I'm still away from:
Avg time       : 69.3088 
http://forum.dlang.org/thread/dpdgcycrgfspcxenzrjf@forum.dlang.org?page=8#post-abncwoqtpnaoohihkliw:40forum.dlang.org

I've tried also 10%, 40% and 80% but 60% seems optimal.

And I think I reached my performance limit. I could implement the 
LazyForwardRange and, if anyone can confirm the statement of char 
<-> dchar decoding and that the usage of ubyte would be (crucial) 
better, I will try this too.