Minor formatting tweaks, comments

Added ImGuiInputTextFlags_CharsNoBlank stock filter. Tweak examples.

ImGuiInputTextFlags_CallbackCharFilter can return 1 to filter character

Added ImGuiInputTextFlags_CharsUppercase stock filter

InputText(): added ImGuiInputTextFlags_CallbackCharFilter system for filtering/replacement. Callback now passed an "EventFlag" parameter.

CalcTextSize*() more optimisation, fast-path for ascii.

CalcTextSize*() tweaks. ImTextCharFromUtf8() return 1 for a zero character now.

CalcTextSize*() functions which are often speed bottleneck for large contents are about 25% faster. ...

Caching character advance contiguously, pulled inline, no int->float
conversion.

Columns offsets cached to avoid repeated binary search.

Added ListBox() (#129) ...

Along with ListBoxHeader(), ListBoxFooter() helpers.

Selectable: fixed text clipping.

Tweaks. Combo default height_in_items is -1 at compilation time to match incoming ListSelect() behavior

Allow passing -0.01f to PushItemWidth() for a perfect right-side alignment + fix CalcItemWidth()

BeginChildFrame() / EndChildFrame() helpers.

PushItemWidth() can take negative value to right-align items. Renamed GetItemWidth() to CalcItemWidth()

Combo() uses Selectable()

Selectable() variant: fixed missed return value

Added BeginChild() variant that takes an ImGuiID

Added Selectable() building block for various list boxes, combo boxes

Internal ButtonBehaviour() supports a pressed_on_click mode (unused yet) + Renamed internal Combo*getters to Items*getters

Tweak default ImGuiCol_HeaderActive to be less bright

Added ImGuiCol_ChildWindowBg, ImGuiStyleVar_ChildWindowRounding for completeness and flexibility ...

Upcoming features using it.

ShowTestWindow() demonstrate tree nodes within columns.

Fixed title bar text clipping issue (fix #128) ...

+ Update version number

Version number

Combo box always appear above other child windows of a same parent

Title bar text uses cpu-clipping + comments

Use cpu-side clipping instead of a new draw call for isolated label-clipped-by-frame cases.

Split RenderText into RenderTextWrapped for internal uses ...

Different text functions with different features (usually orthogonal set
of features)

LabelText: value is properly clipped (fixes #23)