Build by default with optimization level -O2 for GCC

before -O0 was used by default, that caused pretty bad performance.

Amd64, i6700k, 4200MHz, GNU/Linux (non-RT kernel), gcc 7.2.0

-------------------------------------
Optimization | EN/ENO |no EN/ENO |
-------------------------------------
default | 11 | 9.5 |
-O3 | 3.9 | 5.2 |
-O2 | 4 | 4.8 |
-Os | 4.1 | 3.5 |
-Ofast | 3.9 | 5.2 |
-------------------------------------

ARM, BBB Cortex-A8, 600Mhz, GNU/Linux, gcc 4.6.3

-------------------------------------
Optimization | EN/ENO |no EN/ENO |
-------------------------------------
default | 273 | 226 |
-O3 | 141.8 | 106.2 |
-O2 | 142 | 107 |
-Os | 152.5 | 112.2 |
-Ofast | 141.7 | 106.2 |
-------------------------------------

For embedded systems with size constaints (like Cortex-Mx, AVR and so
on) I usually use -Os. It gets pretty good results. For
GNU/Linux-based systems -O2 is usually a good choice, as you see the
test results.

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include yslt.yml2

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in xsl {

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    decl istylesheet (

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        *output="xml",

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        version="1.0",

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        xmlns:xsl="http://www.w3.org/1999/XSL/Transform",

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        xmlns:exsl='http://exslt.org/common',

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        extension-element-prefixes='exsl'

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    ) alias stylesheet {

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        output *output;

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        content;

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    };

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    decl template(match) {

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        content;

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    };

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    decl function(name) alias template {

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        content;

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    };

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    decl call(name) alias call-template {

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        content;

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    };

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    decl apply(select) alias apply-templates {

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        content;

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    };

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}

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