ImGuiTextFilter() can take a default filter string

Sliders: value is clipped inside the frame when resizing sliders to be small.

InputText: size for allowed input size smaller than necessary by 1 byte.

Fix ImFont::BuildLookupTable() potential dangling pointer dereference (fix #131)

ImGuITextFilter::Draw() use regular width call.

Version number + comment

Calculate frame-rate for the user, as a purely luxurious feature ...

..and to reduce sample code size a little.

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.